Tweaks to documentation

[ffl096]

• Adds a link to the GitHub repository to the right of the documentation navbar.
• Replaces the doc source button with a more helpful edit button.
• Add "copy code" button to all examples.
• Add a standard code of conduct.

Depends on pyt-team/TopoNetX#392 (for the code of conduct).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.37%. Comparing base (242dd60) to head (de36a21).
Report is 10 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #285   +/-   ##
=======================================
  Coverage   97.37%   97.37%           
=======================================
  Files          58       58           
  Lines        2059     2059           
=======================================
  Hits         2005     2005           
  Misses         54       54           

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