Clarify in control-spec which relays have ns and md entries and which don't
Over in legacy/trac#14937 (moved) the Tor Browser folks are trying to do a 'getinfo ns/id/...' on a bridge, and of course it's not working because there are no networkstatus stanzas for bridges. But our control-spec just says words like "OR" and "server" so I can't blame them for not intuiting that some ORs have ns entries and some don't.
I also bet the same thing would happen in "getinfo md/id/..." -- we just say "the latest microdescriptor for a given OR." when describing what this feature does.
I'm cc'ing Atagar here too since I bet stem could find this ticket interesting too.