Merge pull request #6 from jonnylamb/readme-fixup

readme: fix path to contribute page

README.md

@@ -1,4 +1,4 @@
 # Web Mirror of Pants Build documentation
 
 To learn where these docs came from and how to change them, please see
-http://pantsbuild.github.io/docs.html and http://pantsbuild.github.io/howto_contrib.html
+http://pantsbuild.github.io/docs.html and http://pantsbuild.github.io/howto_contribute.html