feat: improve contribute section documentation

[moe-ad]

Summary

As stated in the title

Details

The following have been done:

• User, Developer, and Documentarian subsections added to the contribute section.
• Use cases of tox added to Developer and Documentarian subsections.
• Environment variables added to allow exclusion of API and examples during documentation generation in a local environment.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.62%. Comparing base (05c565c) to head (053b4a8).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2085      +/-   ##
==========================================
+ Coverage   86.60%   86.62%   +0.02%     
==========================================
  Files          90       90              
  Lines       10282    10275       -7     
==========================================
- Hits         8905     8901       -4     
+ Misses       1377     1374       -3     

[moe-ad]

Moving to ready for review to check generated documentation

[Revathyvenugopal162]

small suggestions