Document DCO, Signed-off-by requirement

Fixes: #220

Signed-off-by: Nils Philippsen <nils@redhat.com>

DCO.txt

@@ -0,0 +1,34 @@
+Developer Certificate of Origin
+Version 1.1
+
+Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
+
+Everyone is permitted to copy and distribute verbatim copies of this
+license document, but changing it is not allowed.
+
+
+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.

README.rst

@@ -53,6 +53,15 @@ E.g.:
   python run-rpmautospec.py calculate-release bash
 
 
+Contributing
+------------
+
+You need to be legally allowed to submit any contribution to this project. What this
+means in detail is laid out in the file ``DCO.txt`` next to this file. The mechanism by which you
+certify this is adding a ``Signed-off-by`` trailer to git commit log messages, you can do this by
+using the ``--signoff/-s`` option to ``git commit``.
+
+
 ---
 
 License: MIT