Update docstring to explain sample_kwargs + add intersphinx

[drbenvincent]

• Closes add option to choose sampler  #106 by adding info to the docstring to explain sample_kwargs
• Also adds intersphinx, so we can now make clickable links that will take you through directly to the docs of other packages. So far, just PyMC.

Screenshot of local build of the docs:

[codecov]

Codecov Report

Merging #207 (2a1de92) into main (02d2506) will not change coverage.
The diff coverage is n/a.

❗ Current head 2a1de92 differs from pull request most recent head b58c4c2. Consider uploading reports for the commit b58c4c2 to get more accurate results

@@           Coverage Diff           @@
##             main     #207   +/-   ##
=======================================
  Coverage   70.34%   70.34%           
=======================================
  Files          19       19           
  Lines        1005     1005           
=======================================
  Hits          707      707           
  Misses        298      298           

Impacted Files	Coverage Δ
causalpy/pymc_models.py	100.00% <ø> (ø)