Add a new introduction to developing the project

This document extract the parts relevant to development from the
CONTRIBUTING guide and expands it to make it more useful as an
introduction to new developers and people wanting to hack the project.

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>

Author: llucax

cookiecutter/{{cookiecutter.github_repo_name}}/DEVELOPMENT.md

@@ -142,3 +142,4 @@ watch:
   - "{{cookiecutter | src_path}}"
   - README.md
   - CONTRIBUTING.md
+  - DEVELOPMENT.md