Update parquet crate readme

[alamb]

Fixup some out of data information and links that I noticed while reviewing #1082

[codecov-commenter]

Codecov Report

Merging #1192 (5a08392) into master (d68c4ae) will decrease coverage by 0.00%.
The diff coverage is n/a.

❗ Current head 5a08392 differs from pull request most recent head 18e0c16. Consider uploading reports for the commit 18e0c16 to get more accurate results

@@            Coverage Diff             @@
##           master    #1192      +/-   ##
==========================================
- Coverage   82.67%   82.67%   -0.01%     
==========================================
  Files         175      175              
  Lines       51561    51561              
==========================================
- Hits        42630    42629       -1     
- Misses       8931     8932       +1     

Impacted Files	Coverage Δ
arrow/src/array/transform/mod.rs	85.56% <0.00%> (-0.14%)	⬇️

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