Add CONTRIBUTING.md.

Author: nnethercote

CONTRIBUTING.md

@@ -0,0 +1,18 @@
+# Contributing to mctp-rs
+
+If you wish to contribute, please file a pull request with the following
+characteristics.
+
+- Include a `Signed-off-by` trailer on each commit log message to indicate that
+  you agree to the Developer Certificate of Origin (DCO). `git commit -s` makes
+  adding the `Signed-off-by` tag easy.
+
+  In short, this asserts that you have the right to contribute this change -
+  either being your own work, or you are submitting it under a suitable
+  license.
+
+  The text of the DCO is available at <https://developercertificate.org/>
+
+- Pull requests and/or commits that modify a single crate should have a title
+  that begins with that crate's name. E.g. `mctp-estack: Use inbuilt MCTP
+  header parser`.

README.md

@@ -76,3 +76,7 @@ There's a small example MCTP requester in
 ```
 
 There are also some MCTP over serial examples in [standalone/examples](standalone/examples).
+
+Contributing
+------------
+If you wish to contribute, please see the [contribution guidelines](CONTRIBUTING.md).