Update the gitignore and readme to aid contributing

[johndoknjas]

This PR adds some tips to the readme on how contributors can test their changes made to stockfish/models.py. The gitignore is also updated so that executables and a main.py file are ignored in the stockfish folder. Minor updates to some get_wdl_stats stuff is also done.

[github-actions]

Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
stockfish
models.py
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[kieferro]

Looks good, thanks

[johndoknjas]

@kieferro I added one more update to the readme - just putting the new section on contributing right before testing, and then updating the testing section with a tip on how to run things locally with the right path name.

This is how I run the tests on my machine, was just wondering if you do something similar. If so, this may be something we could look into changing, so that contributors can run the test suite without needing to modify the default path in models.py.

[kieferro]

was just wondering if you do something similar

Yes, I do pretty much the same.

this may be something we could look into changing

Yes, I think that's a very good suggestion. Maybe we could use a setup with a command line argument, which is read by test_models.py and then passed as the path for the Stockfish fixture