New triagebot vacation

Author: Noratrieb

src/triagebot/pr-assignment.md

@@ -76,9 +76,11 @@ The existence of the owners table also enables the ability for users to post a c
 
 ### Vacation
 
-If a reviewer wants to temporarily prevent themselves from being assigned (automatically or manually) they can add themselves to the special
+If a reviewer wants to temporarily prevent themselves from being automatically assigned they can add themselves to the special
 `assign.users_on_vacation` group.
 
+They will still be able to be assigned via their name, in which case triagebot will post a warning that the person is on vacation.
+
 ```toml
 [assign]
 users_on_vacation = ["jyn514", "ChrisDenton"]