LICENSE: include DCO notice.

LICENSE

@@ -64,3 +64,37 @@ http://www.gnu.org/licenses/ for a copy) and comes with the following info:
     Project page: http://tuxotronic.org/wiki/projects/stm32loader
 
 -------------------------------------------------------------------------------
+
+Note on contributing patches:
+
+If contributing patches, please add a Signed-off-by: line certifying
+your Developer Certificate of Origin (DCO).  You should include this
+line at the bottom of any Git commits you want merged in, or along
+with any email you submit.  By including this line, you are certifying
+the following:
+
+  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.