Fixed docstrings for graph relabeling and sublattice mapping functionality missing from reference documentation.

[qwriter]

Also, edited those docstrings.

This is the fix for issue https://github.com/dwavesystems/dwave-networkx/issues/234.

Duplicate of #237 because accidentally created PR from main.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 75.81%. Comparing base (0b9682b) to head (5804a5b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #238   +/-   ##
=======================================
  Coverage   75.81%   75.81%           
=======================================
  Files          31       31           
  Lines        2171     2171           
=======================================
  Hits         1646     1646           
  Misses        525      525           

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[JoelPasvolsky]

An advantage of doing a rebase is that you don't get commits like this one scattered through the git history.