A few words on the CLA

Author: jeff5

ProcessDocs/contributor_agreement.md

@@ -0,0 +1,28 @@
+# Contributor Agreement
+
+Jython is a Python Software Foundation project,
+and therefore we use the same process to ensure that
+code submitted by you is actually free for us to use,
+which is this
+[Contributor Agreement](https://www.python.org/psf/contrib/contrib-form/).
+
+Up sides:
+* If you are a contributor to CPython, or its documentation, PEPs etc.,
+  there's nothing else to do.
+* When you have signed up, you're all set to contribute to CPython too. 
+
+Down side:
+* The nice automation of the process built for CPython does not work here
+  (because Jython is not part of the Python GitHub organisation[^1]).
+  So only the manual process works.
+
+When you've signed up,
+add yourself to the ACKNOWLEDGMENTS file in the form
+```
+Real Name (GitHub: githubname)             C, YYYY-MM-DD
+```
+where the date is the current date (date of your sign up).
+
+[^1]: Jython moved to GitHub as its own organisation
+before CPython made the leap.
+