Tidy up to be easier for new contributor to get started#1

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helen-brooks wants to merge 7 commits intomakeclean:masterfrom

helen-brooks:tidy-up

Commits on Oct 3, 2022

Add gitignore file
helen-brooks
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Rename class to avoid name clash; refactor mgga seed into constructor; add some exceptions and tidying
helen-brooks
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Commits on Oct 4, 2022

More usage guidance in README
helen-brooks
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