[options] Mention quoted string literals for --match-filter

youtube_dl/options.py

@@ -302,8 +302,10 @@ def parseOpts(overrideArguments=None):
             'match if the key is present, '
             '!key to check if the key is not present, '
             'key > NUMBER (like "comment_count > 12", also works with '
-            '>=, <, <=, !=, =) to compare against a number, and '
-            '& to require multiple matches. '
+            '>=, <, <=, !=, =) to compare against a number, '
+            'key = \'LITERAL\' (like "uploader = \'Mike Smith\'", also works with !=) '
+            'to match against a string literal '
+            'and & to require multiple matches. '
             'Values which are not known are excluded unless you '
             'put a question mark (?) after the operator. '
             'For example, to only match videos that have been liked more than '