Document remaining commands

[PMunch]

According to https://nim-lang.org/docs/nimsuggest.html only def, con, sug, and use are explained but according to the nimsuggest command we have a longer list (sug|con|def|use|dus|chk|mod|highlight|outline|known). It would be nice to have some explanation of these as well.

[timotheecour]

agreed but please always refer to devel docs (ie https://nim-lang.github.io/Nim/nimsuggest.html) instead of stable when reporting issues (in case issue was fixed in devel; which in this case isnt' the case)