Move "How the extensions work" to OCDS documentation or Extension Explorer

[jpmckinney]

https://github.com/open-contracting/standard_extension_template#how-the-extensions-work

[mrshll1001]

Has there been a decision whether to move this to OCDS Documentation or the Extension Explorer? If so I'm happy to proceed.

[jpmckinney]

Let's move it to the Extension Explorer. You can find a place for it in this doc (still need to put it into website templates): https://docs.google.com/document/d/1JQCOQzLvwEeue6yE4AugyPXQlsC08-ljfUoBwJ4bNWQ/edit

[jpmckinney]

Noting that the above document has been integrated into the website in open-contracting/extension-explorer#47