rfcbot should warn if issue/PR isn't tagged

[alexcrichton]

I believe rfcbot requires a T-foo tag, but if one's missing it could perhaps leave a comment saying so if someone starts an FCP with @rfcbot fcp merge

[anp]

I'm thinking that this will need an additional check -- not just "is the command from someone on a tagged team?" If they aren't on a tagged team (whether there are any tagged teams or not), we should check "are they on any team at all?" before putting a comment up. In other words, non-team-members shouldn't be able to have rfcbot spam issue threads.

[alexcrichton]

👍