[options] Update help on string comparisons

youtube_dl/options.py

@@ -298,7 +298,9 @@ def parseOpts(overrideArguments=None):
             ' brackets, as in -f "best[height=720]"'
             ' (or -f "[filesize>10M]"). '
             ' This works for filesize, height, width, tbr, abr, vbr, and fps'
-            ' and the comparisons <, <=, >, >=, =, != .'
+            ' and the comparisons <, <=, >, >=, =, !='
+            ' and for ext, acodec, vcodec, container and protocol'
+            ' and the comparisons =, != .'
             ' Formats for which the value is not known are excluded unless you'
             ' put a question mark (?) after the operator.'
             ' You can combine format filters, so  '