Extend docs for qualified names by new features from #477

[zsol]

Summary

Documentation changes.

Test Plan

look at the generated docs

[codecov-commenter]

Codecov Report

Merging #478 (ee34e13) into master (068b905) will decrease coverage by 0.00%.
The diff coverage is 94.59%.

@@            Coverage Diff             @@
##           master     #478      +/-   ##
==========================================
- Coverage   94.68%   94.68%   -0.01%     
==========================================
  Files         236      236              
  Lines       22978    23013      +35     
==========================================
+ Hits        21757    21790      +33     
- Misses       1221     1223       +2     

Impacted Files	Coverage Δ
libcst/metadata/scope_provider.py	95.72% <90.00%> (-0.22%)	⬇️
libcst/metadata/tests/test_name_provider.py	100.00% <100.00%> (ø)

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[zsol]

For your reviewing pleasure: https://9786-200896124-gh.circle-artifacts.com/0/doc/metadata.html#libcst.metadata.Scope.get_qualified_names_for

[jimmylai]

LGTM

@zsol , regarding to your comments on #477,
do you still plan to provide QualifiedName for imports and update RenameCommand?