Round out documentation for users, new lab members, and basic new dev dox

There is currently no wiki info about umil, linkedmusic, wikidata, or... anything. this issue is specifically towards working on adding documentation to get a new UMIL user, new lab hire/member, or a new dev situated in what's going on broadly.

@JoyfulGen looping you in on this, because you've gone through this recently, and are also going to be QAing quite a bit! Also calling on @kyuchia for your thoughts on things that need documentation; both of you probably have some great insights for how to find instruments, if you wanted to start a new page about finding instruments at large or on Wikidata (if wikidata, I will add a specific subpage about this in the wiki under wikidata; "musical instruments in wikidata" > finding instruments / adding new instrument(s)/names"