Document our extensions/providers extend the API

[zanate4019]

This issue tracker is for documentation

For product issues, use https://github.com/aspnet/EntityFramework/issues

[ajcvickers]

@zanate4019 Can you be more specific what you mean by, "DbContextOptions options available"?

[zanate4019]

Sorry Arthur, I don't remember what I was researching when I posted that 6 months ago ;)