Document how to create a new mapping commons using cookiecutter

[matentzn]

@hrshdhgd would you be able to add a documentation page here https://github.com/mapping-commons/sssom/tree/master/src/docs called create-mapping-commons.md and fill it with some initial instructions and

1. how to create a new mapping commons from zero to hero and
2. how to update one

We have a new team member (@ehartley) who will help us building the template up.

[hrshdhgd]

Do you mean using https://github.com/mapping-commons/mapping-commons-cookiecutter ?

[matentzn]

Sorry I meant to share that link! Yes exactly!

[hrshdhgd]

Started a stub: mapping-commons/sssom-py#374

I don't know what the end product is supposed to look like.

[matentzn]

Thanks for getting this started. I would prefer this lives in the SSSOM repo in the docs, not sssom py. Can you move it? I will comment on it later. Thanks!

[hrshdhgd]

Completely messed that up. Sorry! #277