Fix the section name in CONTRIBUTING.rst

The name of the section 'If you'are developer, start here'
has changed in the wiki. This commit updates it to correctly
refer to the good section.

Change-Id: Ief8c1e3dfa75baea945b8c094f17e20183e7f44b
Closes-bug: #1332915
Fixed the reference to 'Creating Unit Tests' in HACKING.rst

Change-Id: Ie9778aceabb4239058468cf64009792253995ec2
Closes-bug: #1332920
Merge "Fixed the reference to 'Creating Unit Tests' in HACKING.rst"
Merge "Fix the section name in CONTRIBUTING.rst"