Merge branch 'forking-doc' into 'master'

Documentation on how to fork a project

Added documentation on how to fork a project.

/cc @sabba

See merge request !1623

doc/workflow/README.md

 # Workflow
 
 - [Feature branch workflow](workflow.md)
+- [Code forking workflow](forking_workflow.md)
 - [Project Features](project_features.md)
 - [Authorization for merge requests](authorization_for_merge_requests.md)
 - [Groups](groups.md)

doc/workflow/forking_workflow.md

+# Code forking workflow
+
+Forking a project to your own namespace is useful if you have no write access to the project you want to contribute
+to. If you do have write access or can request it we recommend working together in the same repository since it is simpler.
+See our **[GitLab Flow](https://about.gitlab.com/2014/09/29/gitlab-flow/)** article for more information about using
+branches to work together.
+
+## Creating a fork
+
+In order to create a fork of a project, all you need to do is click on the fork button located on the top right side
+of the screen, close to the project's URL and right next to the stars button.
+
+![Fork button](forking/fork_button.png)
+
+Once you do that you'll be presented with a screen where you can choose the namespace to fork to. Only namespaces
+(groups and your own namespace) where you have write access to, will be shown. Click on the namespace to create your
+fork there.
+
+![Groups view](forking/groups.png)
+
+After the forking is done, you can start working on the newly created repository. There you will have full
+[Owner](../permissions/permissions.md) access, so you can set it up as you please.
+
+## Merging upstream
+
+Once you are ready to send your code back to the main project, you need to create a merge request. Choose your forked
+project's main branch as the source and the original project's main branch as the destination and create the merge request.
+
+![Selecting branches](forking/branch_select.png)
+
+You can then assign the merge request to someone to have them review your changes. Upon pressing the 'Accept Merge Request'
+button, your changes will be added to the repository and branch you're merging into.
+
+![New merge request](forking/merge_request.png)
+
+