[DOC] add missing dataset document

[szha]

Description

add missing dataset document. resolves #831

Checklist

Essentials

• PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented

Changes

• add missing dataset document

[mli]

Found link check problems in job PR-832/1:
(line 7) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 4) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 4) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 3) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 4) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 4) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 7) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 4) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 4) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 19) broken https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/ - 404 Client Error: Not Found for url: https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/
(line 5) broken https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/ - 404 Client Error: Not Found for url: https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/
(line 5) broken https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/ - 404 Client Error: Not Found for url: https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/
(line 21) broken https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/ - 404 Client Error: Not Found for url: https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/
(line 442) broken https://www.aclweb.org/anthology/P02-1040.pdf)[1 - 404 Client Error: Not Found for url: https://www.aclweb.org/anthology/P02-1040.pdf)%5B1
(line 92) broken https://nlp.stanford.edu/pubs/glove.pdf)[2 - 404 Client Error: NOT FOUND for url: https://nlp.stanford.edu/pubs/glove.pdf)%5B2
(line 208) broken https://www.bioinf.jku.at/publications/older/2604.pdf)[3 - 404 Client Error: Not Found for url: https://www.bioinf.jku.at/publications/older/2604.pdf)%5B3

[mli]

Job PR-832/1 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-832/1/index.html

[codecov]

Codecov Report

Merging #832 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #832      +/-   ##
==========================================
- Coverage   90.48%   90.43%   -0.05%     
==========================================
  Files          66       66              
  Lines        6348     6348              
==========================================
- Hits         5744     5741       -3     
- Misses        604      607       +3

Impacted Files	Coverage Δ
src/gluonnlp/data/utils.py	74.14% <0%> (-2.05%)	⬇️

[mli]

Found link check problems in job PR-832/2:
(line 4) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 3) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 4) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 4) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 4) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 7) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 7) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 4) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 4) broken https://gluebenchmark.com/tasks - 404 Client Error: Not Found for url: https://gluebenchmark.com/tasks
(line 19) broken https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/ - 404 Client Error: Not Found for url: https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/
(line 5) broken https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/ - 404 Client Error: Not Found for url: https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/
(line 5) broken https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/ - 404 Client Error: Not Found for url: https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/
(line 21) broken https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/ - 404 Client Error: Not Found for url: https://www.salesforce.com/products/einstein/ai-research/the-wikitext-dependency-language-modeling-dataset/
(line 442) broken https://www.aclweb.org/anthology/P02-1040.pdf)[1 - 404 Client Error: Not Found for url: https://www.aclweb.org/anthology/P02-1040.pdf)%5B1
(line 92) broken https://nlp.stanford.edu/pubs/glove.pdf)[2 - 404 Client Error: NOT FOUND for url: https://nlp.stanford.edu/pubs/glove.pdf)%5B2
(line 208) broken https://www.bioinf.jku.at/publications/older/2604.pdf)[3 - 404 Client Error: Not Found for url: https://www.bioinf.jku.at/publications/older/2604.pdf)%5B3

[mli]

Job PR-832/2 is complete.
Docs are uploaded to http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR-832/2/index.html