Add how to on many to may relationships - Fixes #148

[EspenBrun]

Proposed Changes

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• [ ] Bugfix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
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Further comments

I have not generated the html, would be nice to get help with that.

I used ResizeArray and not ICollection. I get an error when I use ICollection.

[EspenBrun]

148

[simon-reynolds]

Hi @EspenBrun Thank you for the PR, any extra documentation is always appreciated!