Adds a contributing file (#3)

Fixes #2

Signed-off-by: Chuck Ha <[email protected]>

CONTRIBUTING.md

@@ -0,0 +1,59 @@
+# Contributing
+
+## DCO Sign off
+
+All authors to the project retain copyright to their work. However, to ensure
+that they are only submitting work that they have rights to, we are requiring
+everyone to acknowledge this by signing their work.
+
+Any copyright notices in this repo should specify the authors as "the Heptio Sonobuoy project contributors".
+
+To sign your work, just add a line like this at the end of your commit message:
+
+```
+Signed-off-by: Joe Beda <[email protected]>
+```
+
+This can easily be done with the `--signoff` option to `git commit`.
+
+By doing this you state that you can certify the following (from https://developercertificate.org/):
+
+```
+Developer Certificate of Origin
+Version 1.1
+
+Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
+1 Letterman Drive
+Suite D4700
+San Francisco, CA, 94129
+
+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.
+```