Add specific contribution guidelines for documentation

[sgibson91]

This was an idea that came out of a documentation workshop at the Collaborations Workshop run by the Software Sustainability Institute.

For new users coming to contribute to a project, they are the mostly likely candidates to find gaps in your documentation and potentially come up with solutions to these gaps. Therefore, I'm proposing a section in CONTRIBUTING.md that outlines the process by which to update the docs, including:

• opening an issue to discuss the change or document the knowledge gap if they themselves can't fill it
• where do the sources files for the docs live
  • this may include an "improve this page" style link on the host website which links to the repo, distinct from the "Page source" link currently implemented
• how to locally compile the docs to preview your changes before making a pull request

I hope you think this is a good idea, I think it will encourage even more people to get involved! :)

[sgibson91]

This could probably just be a summary of the Jupyter contribution guidelines for documentation with the specific make command to locally compile 😄

[betatim]

I think this is a great idea! I think we should have a short version of this guide in https://github.com/jupyterhub/binderhub/blob/master/CONTRIBUTING.md which describes the steps you mentioned with the commands you can copy&paste. And then a link to the longer version at https://jupyter.readthedocs.io/en/latest/contrib_docs/index.html.

Even as an experienced contributor I find the full version quite overwhelming and "oh my god where do i even start?" where as if you give me a bullet point list with ten steps that fits on one screen I am "ok, easy peasy, this will take 5minutes" (even though it usually takes longer, but at least I get started).

[sgibson91]

@betatim I think you addressed this in #824 and can be closed