Create a style guide

[fmichonneau]

as suggested in #258

having a style guide would be useful to ensure that contributions from different community members are consistent and inclusive.

[TomKellyGenetics]

To clarify I think some aspects specific to each language will be necessary. If there is a style guide in English and some general points applying to all contributions that would be a helpful starting point though.

We've discussed some consistent style decisions amongst the contributors for Japanese. As the number of contributors increases, it would be good to have somewhere to document these guidelines for new contributors to avoid them feeling they made a mistake during reviews.

Have you considered how you document a style guide? We've been considering using "Read The Docs" (which supports multilingual versions) for other projects as used for this repository:

https://github.com/carpentries-i18n/i18n-handbook
https://carpentries-i18n-handbook.readthedocs.io/en/latest/