docs(CONTRIBUTING.md): Add CLA section
# Contributing Guidlines
The OSM project accepts contributions via GitHub pull requests. This document outlines the requirements for contributing to this project.
+## Contributor License Agreement
+
+This repository is governed under a [Contributor License Agreement](https://cla.opensource.microsoft.com/open-service-mesh/osm). All PR submitters must accept the CLA before their contributions can be merged.
+
## Roadmap
We use [GitHub Project Boards](https://github.com/open-service-mesh/osm/projects) to help give a high level overview and track what work is going on and what stage it is in. If you want an idea of our roadmap and prioritization, this is the best place to find that information.
