Clarify help of --write-pages (#1853)

youtube_dl/__init__.py

@@ -317,7 +317,7 @@ def parseOpts(overrideArguments=None):
             help='print downloaded pages to debug problems(very verbose)')
     verbosity.add_option('--write-pages',
             action='store_true', dest='write_pages', default=False,
-            help='Write downloaded pages to files in the current directory')
+            help='Write downloaded intermediary pages to files in the current directory to debug problems')
     verbosity.add_option('--youtube-print-sig-code',
             action='store_true', dest='youtube_print_sig_code', default=False,
             help=optparse.SUPPRESS_HELP)