Add PR template

Author: quicklisp

.github/pull_request_template.md

@@ -0,0 +1,10 @@
+# No pull requests
+
+Please do not create pull requests for this repo.
+
+If you would like to add, remove, or modify a project in Quicklisp,
+please [open an
+issue](https://github.com/quicklisp/quicklisp-projects/issues)
+instead.
+
+If you have any questions, feel free to [email me](mailto:zach@quicklisp.org).