Cherry pick Add some doc comments to parquet bit_util to active_release

[alamb]

Automatic cherry-pick of 7b2e26d

• Originally appeared in Add some doc comments to parquet bit_util #663: Add some doc comments to parquet bit_util

[codecov-commenter]

Codecov Report

Merging #678 (32df29b) into active_release (ead64b7) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@                Coverage Diff                 @@
##           active_release     #678      +/-   ##
==================================================
- Coverage           82.38%   82.38%   -0.01%     
==================================================
  Files                 167      167              
  Lines               46471    46471              
==================================================
- Hits                38286    38285       -1     
- Misses               8185     8186       +1     

Impacted Files	Coverage Δ
parquet/src/util/bit_util.rs	93.14% <ø> (ø)
parquet/src/encodings/encoding.rs	94.48% <0.00%> (-0.20%)	⬇️

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