Add link to feature request hartator#26

Author: hartator

README.md

@@ -48,3 +48,5 @@ To run the tests:
 
     bundle install
     bundle exec rake test
+    
+If you want to help but you don't know where to start, you can work on  [this]( https://github.com/hartator/wayback-machine-downloader/issues/26).