Update CONTRIBUTING.md to reflect current state

Author: Student Main

CONTRIBUTING.md

@@ -7,13 +7,12 @@ Pull Requests
 1. Pull requests are welcome.
 2. Make sure to pass the unit tests. Write unit tests for new modules if
 needed.
+3. Search before sending new pull request.
 
 Issues
 ------
 
-1. Nobody has reported any bugs but posted a lot of questions in the last
-few months. So we're closing the issue tracker.
+1. **DO NOT post question about connection problem in issue tracker**, read [Troubleshooting].
+2. Search before sending new issue.
 
-
-[Troubleshooting]: https://github.com/clowwindy/shadowsocks/wiki/Troubleshooting
-[mailing lists]:   https://groups.google.com/forum/#!forum/shadowsocks
+[Troubleshooting]: https://github.com/shadowsocks/shadowsocks-windows/wiki/Troubleshooting