Add developer certificate of origin docs

Signed-off-by: Ben Firshman <[email protected]>

CONTRIBUTING.md

@@ -1,5 +1,7 @@
 # Contributing to Fig
 
+## Development environment
+
 If you're looking contribute to [Fig](http://orchardup.github.io/fig/)
 but you're new to the project or maybe even to Python, here are the steps
 that should get you started.
@@ -27,4 +29,47 @@ OS X:
 
 Note that this only works on Mountain Lion, not Mavericks, due to a [bug in PyInstaller](http://www.pyinstaller.org/ticket/807).
 
+## Sign your work
+
+The sign-off is a simple line at the end of the explanation for the
+patch, which certifies that you wrote it or otherwise have the right to
+pass it on as an open-source patch.  The rules are pretty simple: if you
+can certify the below (from [developercertificate.org](http://developercertificate.org/)):
+
+    Developer's Certificate of Origin 1.1
+
+    By making a contribution to this project, I certify that:
+
+    (a) The contribution was created in whole or in part by me and I
+        have the right to submit it under the open source license
+        indicated in the file; or
+
+    (b) The contribution is based upon previous work that, to the best
+        of my knowledge, is covered under an appropriate open source
+        license and I have the right under that license to submit that
+        work with modifications, whether created in whole or in part
+        by me, under the same open source license (unless I am
+        permitted to submit under a different license), as indicated
+        in the file; or
+
+    (c) The contribution was provided directly to me by some other
+        person who certified (a), (b) or (c) and I have not modified
+        it.
+
+    (d) I understand and agree that this project and the contribution
+        are public and that a record of the contribution (including all
+        personal information I submit with it, including my sign-off) is
+        maintained indefinitely and may be redistributed consistent with
+        this project or the open source license(s) involved.
+
+then you just add a line saying
+
+    Signed-off-by: Random J Developer <[email protected]>
+
+using your real name (sorry, no pseudonyms or anonymous contributions.)
+
+The easiest way to do this is to use the `--signoff` flag when committing. E.g.:
+
+
+    $ git commit --signoff