;doc:Special tags: note type: as another one to avoid

Author: simonmichael

hledger/hledger.m4.md

@@ -1645,7 +1645,7 @@ You can declare valid tag names with the [tag directive](#tag-directive) and the
 ### Special tags
 
 Some tag names have special significance to hledger.
-There's not much harm in using them yourself, but some could produce an error message, particularly the `date:` tag.
+There's not much harm in using them yourself, but some could produce an error message, particularly the `date:` and `type:` tags.
 They are explained elsewhere, but here is a quick list for reference:
 
 <!-- keep synced with JournalChecks.hs -->