Add to discogs plugin docs regarding PR
Clarify basic search behaviour in intro chapter of discogs plugin,
and state change introduced in PR#4227 (discogs: Discogs query on
insufficiently tagged files)
@@ -19,7 +19,8 @@ authentication credentials via a personal access token or an OAuth2
authorization.
Matches from Discogs will now show up during import alongside matches from
-MusicBrainz.
+MusicBrainz. The search terms sent to the Discogs API are based on the artist
+and album tags of your tracks. If those are empty no query will be issued.
If you have a Discogs ID for an album you want to tag, you can also enter it
at the "enter Id" prompt in the importer.
