Add to docs: PostGraphile supports any authentication that Node supports.

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Arguably it's also a "bug in documentation" bug report: your choice:)

It just seems like there should be *something*, *somewhere*, which explains whether committing to Postgraphile means committing to local user accounts, or whether it's possible to combine the library with OAuth (eg. Google's, Facebook's, etc.).

Start by reviewing the PostGraphile documentation for authentication and the Node authentication context described in the issue. Document whether OAuth providers such as Google and Facebook can be combined with PostGraphile, and make the answer easy to find. Done when the docs clearly state the authentication options and whether local accounts are required.

Scritto dal modello di indicizzazione a partire dal testo della issue.