Start documenting the sign-off procedure in SubmittingPatches

We already have over 200 sign-off lines in the kernel, so
let's document the thing, even if discussion may still be
on-going.

Documentation/SubmittingPatches

@@ -259,6 +259,47 @@ e-mail discussions.
 
 
 
+11) Sign your work
+
+To improve tracking of who did what, especially with patches that can
+percolate to their final resting place in the kernel through several
+layers of maintainers, we've introduced a "sign-off" procedure on
+patches that are being emailed around.
+
+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 a open-source patch.  The rules are pretty simple: if you
+can certify the below:
+
+        Developer's Certificate of Origin 1.0
+
+        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.
+
+then you just add a line saying
+
+	Signed-off-by: Random J Developer <random@developer.org>
+
+Some people also put extra tags at the end.  They'll just be ignored for
+now, but you can do this to mark internal company procedures or just
+point out some special detail about the sign-off. 
+
+
 -----------------------------------
 SECTION 2 - HINTS, TIPS, AND TRICKS
 -----------------------------------