Add CONTRIBUTING.md

github evaluates the maturity of a project in part by whether it has
certain things set up: a readme, a license, a contributions document
and a code of conduct.  There's no cost to adding the CONTRIBUTING.md
which the github mirror will pick up - it's the content from a web page
(and points to that page as well).

Change-Id: Idb77d3b822482ddc430cf500eca0a6bae5ccc955
Signed-off-by: Mats Wichmann <mats@linux.com>
(cherry picked from commit 140f1b9f)

CONTRIBUTING.md

+# Get Involved
+
+There are many ways to get involved in the IoTivity community, not all involve contributing code. Follow the links below to start participating!
+
+* [Project Governance](https://www.iotivity.org/about/project-governance)
+* [Create an account](https://www.iotivity.org/user)
+* [Submit patches](https://wiki.iotivity.org/submitting_to_gerrit) (review the [Contribution Guidelines](https://www.iotivity.org/get-involved/contribution-guidelines))
+* [Review submissions by others](https://wiki.iotivity.org/reviewing_patches)
+* [File bugs](https://jira.iotivity.org)
+* [Document feature requests](https://www.iotivity.org/get-involved/feature-development)
+* Subscribe to the [mailing lists](http://lists.iotivity.org)
+* Participate in the IRC Channel on freenode \#iotivity
+* Contribute to the [wiki documentation](https://wiki.iotivity.org/)
+* Follow along with the [blog](https://www.iotivity.org/blog) and [Twitter](https://twitter.com/IoTivity)
+
+# Feature Development
+
+Learn how new features for IoTivity are submitted.
+[Here's how](https://www.iotivity.org/get-involved/feature-development)
+
+# Contribution Guidelines
+
+Learn how to contribute code to the IoTivity project.
+[Here's how](https://www.iotivity.org/get-involved/contribution-guidelines)
+
+> Note: the master copy of this document lives at https://www.iotivity.org/get-involved