Update contribution guide
Description
This MR provides information for users looking to open an issue to fix or report and issue with BuildStream.
Changes proposed in this merge request:
- Add a link to the user to open a new issue
- Add a link to the policies document from then "no-software" repo
- Rename from HACKING to CONTRIBUTING in order for the Gitlab UI to better integrate the contribution guide
This merge request, when approved, will close issue/bug:
Edited by Adam Jones