Add content relevant to passing extension review from internal process document

[duncandewhurst]

Follow up issue to #47. Copying relevant comments:

• Add content relevant to passing extension review (see internal process document)
• Consider which of the review criteria to add to the readmes of the extension registry or extension template

I've integrated the criteria from the 'quick checks' section of the process note, but left the 'in-depth checks'. Potentially, we could add the criteria under the 'individual files' subheading to the extension registry readme.

I'm not sure which heading you're referring to. Do you mean under each subheading under this heading in the template's repo? https://github.com/open-contracting/standard_extension_template#extension-repository-structure

Ah sorry, I was referring to the headings in the process note. I've integrated the quick checks, but left the in depth checks. My suggestion was to add the content from the individual files subheading to the extension registry readme - I hadn't thought about where exactly in the readme to put it, though.

Right - I don't think it belongs in the registry repo, if the goal is for publishers to author good quality extensions (whether registered or not). I thought maybe it'd work better in the extension template repo (though if we move content out of there, then it probably makes sense to put it in the Extension Explorer).