[twitter] update docs for 'quoted' & 'unique'

docs/configuration.rst

@@ -2691,6 +2691,13 @@ Default
 Description
     Fetch media from quoted Tweets.
 
+    If the value is ``true``, then gallery-dl will try to fetch
+    the quoted (original) Tweet when it sees the Tweet which quotes it.
+
+    Note: If the original Tweet later appears again in the timeline
+    (e.g. the author quoted their own Tweet), it will be handled
+    according to the `unique <extractor.twitter.unique_>`__ option.
+
 
 extractor.twitter.replies
 -------------------------
@@ -2767,6 +2774,10 @@ Default
 Description
     Ignore previously seen Tweets.
 
+    If this option is ``false``, the Tweets may or may not be skipped
+    depending on the `archive-format <extractor.*.archive-format_>`__
+    you use.
+
 
 extractor.twitter.users
 -----------------------