Add branch naming and issue labeling rules to documentation

[SergioLuis]

Assigned people

Developer: @mikelcaz
Reviewer: @SergioLuis

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Description

This is what Mikel & Sergio agreed on, on thursday 5th of July, 2018. Adapt it as necessary, and add it to the Contributing wiki page:

# Branch naming / Issue labeling

* feature -> Something that the user is going to be able to use directly.
* hotfix -> Something that affects the expected behavior and it has been already released in a golden build.
* fix -> Something that affects the expected behavior, but it has not been released, or it has been shipped in an alpha/beta build channel.
* topic -> Everything else that does not fit the above categories.

Note: add the new section as a comment to this issue first. Then, once we both are happy with the changes, copy and paste it to the Wiki.