Add note about @ mentions in maintainer docs
Add note about @ mentions in maintainer docs

Thanks @beardofedu for the reminder on this one.

tejasbubane/exercism.io,mhelmetag/exercism.io,nathanbwright/exercism.io,treiff/exercism.io,treiff/exercism.io,RaptorRCX/exercism.io,tejasbubane/exercism.io,nathanbwright/exercism.io,mhelmetag/exercism.io,treiff/exercism.io,jtigger/exercism.io,jtigger/exercism.io,tejasbubane/exercism.io,treiff/exercism.io,jtigger/exercism.io,RaptorRCX/exercism.io,mhelmetag/exercism.io,tejasbubane/exercism.io,RaptorRCX/exercism.io,mhelmetag/exercism.io,nathanbwright/exercism.io,RaptorRCX/exercism.io,jtigger/exercism.io,nathanbwright/exercism.io