Adds PR Template

[BradyPlanden]

This adds:

• A PR template
• Additional nox sessions for easier development
  • run all standard test (unit, integration, examples, notebooks) ->nox -s tests
  • run the doc tests -> nox -s doctest
  • run the above two as one -> nox -s quick
  • run pre-commit -> nox -s pre-commit
• Bugfix doc builds where path was not set correctly.

This needs to be merged after #139, and closes #185.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.34%. Comparing base (93f33e6) to head (02ee2e2).
Report is 59 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #214      +/-   ##
===========================================
+ Coverage    94.29%   94.34%   +0.04%     
===========================================
  Files           32       32              
  Lines         1614     1661      +47     
===========================================
+ Hits          1522     1567      +45     
- Misses          92       94       +2     

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[agriyakhetarpal]

All of these changes look reasonable, thanks, @BradyPlanden!