clarify how to load the dbpedia vector embeddings into a postgres database

[Bodobolero]

Problem

Improve the readme for the data load step in the pgvector performance test.

[github-actions]

3144 tests run: 3011 passed, 0 failed, 133 skipped (full report)

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Code coverage* (full report)

• functions: 31.4% (6448 of 20543 functions)
• lines: 48.3% (49953 of 103355 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
8bf7ad6 at 2024-05-28T14:19:22.219Z :recycle:}