[README] Fix VALID_URL in extractor example

README.md

@@ -384,10 +384,10 @@ If you want to add support for a new site, you can follow this quick list (assum
         import re
 
         from .common import InfoExtractor
-
+        
-
+        
         class YourExtractorIE(InfoExtractor):
-            _VALID_URL = r'https?://(?:www\.)yourextractor\.com/watch/(?P<id>[0-9]+)'
+            _VALID_URL = r'https?://(?:www\.)?yourextractor\.com/watch/(?P<id>[0-9]+)'
             _TEST = {
                 'url': 'http://yourextractor.com/watch/42',
                 'md5': 'TODO: md5 sum of the first 10KiB of the video file',