META: Improve all extensions' documentation

[jpmckinney]

The newest extensions (from work on the OCDS for EU profile) follow a consistent format. There can sometimes be more expansion of their use cases, but in general they are fairly straightforward.

The quality and format of some earlier extensions' documentation is inconsistent.

This issue is about:

• Identify the best examples of extension documentation
• Create a backlog of extensions that need improvement
• Work through them one at a time

Then, Duncan can review for correctness (hopefully quick), and James can do a final review for style and consistency.

[ColinMaudry]

I may have missed something, but I think the latest extensions miss a link to their page in the extension explorer (ex https://extensions.open-contracting.org/en/extensions/awardCriteria/master/). That would be a useful addition to extension's READMEs.

[ColinMaudry]

Ah, we have used the Github "website" field to document the page in the extension explorer. That's good, but I'm not sure people will find it (I had forgotten about it).

[jpmckinney]

I can check the analytics, but I don't think many people visit the extensions on GitHub – we expect people to always use the Extension Explorer.