Development workflow guide.

[malishav]

This issue should add a development guide to the documentation:

• Overall workflow from issue creation to PR merge, issue reopening etc.
• Branch naming convention in the format tag/description (e.g. docs/development-workflow)
• Commit naming convention, e.g. each commit prefixed by #i, where i is the issue number
• PR description: mandatory explicative title and a short description of the work done