Added documentation on how to add compatibility tests

[VictorKoenders]

Rendered

[codecov]

Codecov Report

Merging #497 (f29c2e8) into trunk (9d70b8c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##            trunk     #497   +/-   ##
=======================================
  Coverage   68.35%   68.35%           
=======================================
  Files          43       43           
  Lines        3049     3049           
=======================================
  Hits         2084     2084           
  Misses        965      965           

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[gimbling-away]

https://gist.github.com/Yush08/a35de1de33c0f9fcc5dc7319c281261b

Here's a few grammatical edits.