Move contributing section to its own file

For our friends who find things on github, having a file called
CONTRIBUTING.rst is helpful, as it displays as instructions (that
likely no one will read) in the pull request create screen.

Change-Id: Ifcb28600ccc8919a298639c018f6b49eddb7f4ee

CONTRIBUTING.rst

@@ -0,0 +1,13 @@
+To browse the latest code, see: https://git.openstack.org/cgit/stackforge/gertty/tree/
+To clone the latest code, use `git clone git://git.openstack.org/stackforge/gertty`
+
+Bugs are handled at: https://storyboard.openstack.org/
+
+Code reviews are handled by gerrit at: https://review.openstack.org
+
+Use `git review` to submit patches (after creating a gerrit account
+that links to your launchpad account). Example::
+
+    # Do your commits
+    $ git review
+    # Enter your username if prompted

README.rst

@@ -97,16 +97,5 @@ to the program:
 Contributing
 ------------
 
-To browse the latest code, see: https://git.openstack.org/cgit/stackforge/gertty/tree/
-To clone the latest code, use `git clone git://git.openstack.org/stackforge/gertty`
-
-Bugs are handled at: https://storyboard.openstack.org/
-
-Code reviews are handled by gerrit at: https://review.openstack.org
-
-Use `git review` to submit patches (after creating a gerrit account
-that links to your launchpad account). Example::
-
-    # Do your commits
-    $ git review
-    # Enter your username if prompted
+For information on how to contribute to gertty, please see the
+contents of the CONTRIBUTING.rst file.