update docs to reflect recent changes (joins and window functions)

[jimexist]

Which issue does this PR close?

update docs to reflect recent changes (joins and window functions)

Closes #.

Rationale for this change

this original description is now stale

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #489 (b583042) into master (4c7d418) will decrease coverage by 0.00%.
The diff coverage is n/a.

❗ Current head b583042 differs from pull request most recent head 63ca3f3. Consider uploading reports for the commit 63ca3f3 to get more accurate results

@@            Coverage Diff             @@
##           master     #489      +/-   ##
==========================================
- Coverage   82.65%   82.65%   -0.01%     
==========================================
  Files         165      165              
  Lines       45524    45524              
==========================================
- Hits        37628    37627       -1     
- Misses       7896     7897       +1     

Impacted Files	Coverage Δ
parquet/src/encodings/encoding.rs	94.85% <0.00%> (-0.20%)	⬇️

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[alamb]

Thanks @jimexist