Add contribution guide

CONTRIBUTING.md

+## Write for GitLab
+
+
+Find out more about how you can [Write for GitLab](https://about.gitlab.com/community/writers/).
+
+The posts themselves are published in the [Gitlab.com project](https://gitlab.com/gitlab-com/www-gitlab-com)
+There the blog posts are drafted, commented on and merged. 
+
+### View the backlog of issues
+
+* [View High priority issues](https://gitlab.com/gitlab-com/blog-posts/issues?label_name=High+priority)
+* High level [Technical overviews](https://gitlab.com/gitlab-com/blog-posts/issues?label_name=Technical+overview) which explain the "why" behind something and how it all works.
+* [Decision maker](https://gitlab.com/gitlab-com/blog-posts/issues?label_name=Decision+maker) topics which help people understand benefits and trade-offs.
+* Step by step [Tutorials](https://gitlab.com/gitlab-com/blog-posts/issues?label_name=Tutorial)
+
+As well as topics related to the people behind the projects, collaboration, etc. 
+
+* [Open source](https://gitlab.com/gitlab-com/blog-posts/issues?label_name=Open+source)
+* [Community](https://gitlab.com/gitlab-com/blog-posts/issues?label_name=Community)
+
+### Apply
+
+Submit your application to the program: [Write for GitLab](https://about.gitlab.com/community/writers/).
+
+### Write
+
+When an issue is assigned, that means it's being worked on. You will be assigned an issue to write. 
+
+