Add support for community contributions

[maxrjones]

This PR add components that will enable community contributions:

• adds a code of conduct linking to https://github.com/pangeo-data/governance/blob/master/conduct/code_of_conduct.md
• adds sections on contributing code, documentation, and CI to the contributing guide (modified from xarray's guide )
• sets up issue/PR templates (modified from xarray issue templates and PyGMT PR template)
• adds xbatcher.show_versions (modified from PyGMT)

Closes #32
Closes #44

[codecov]

Codecov Report

Merging #79 (5b817a4) into main (653c3e4) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #79   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         4    +1     
  Lines          136       159   +23     
  Branches        32        35    +3     
=========================================
+ Hits           136       159   +23     

Impacted Files	Coverage Δ
xbatcher/util/print_versions.py	100.00% <100.00%> (ø)

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[andersy005]

This looks great to me 👍🏽

[andersy005]

Do we want to relax the codecov requirements for the CI to pass?

[maxrjones]

Thanks for the quick review @andersy005! I'll modify the tests to improve code coverage before merging. I plan to submit another PR to drop 3.7 support and test on 3.10 following NEP 0029, so I think we can ignore that failure.