doc: add README.rst especially for github

Apparently README.rst overrides README, so this will show up instead
of our generic README on github.

If the user is already on github, then clicking a link for more
information is not a hardship.

diff --git a/README.rst b/README.rst
new file mode 100644 (file)
index 0000000..4009328
--- /dev/null
+++ b/README.rst
@@ -0,0 +1,11 @@
+If you're reading this on github.com, this is a read-only mirror of
+the notmuch project.
+
+For more information about the project, see http://notmuchmail.org.
+
+Please don't send us pull requests on github. If you have a feature
+branch that you want us to look at, use ``git send-email`` to it send
+to notmuch@notmuchmail.org.
+
+For more information about contributing to the project, see
+http://notmuchmail.org/contributing/.