Merge pull request #21 from htgoebel/master

Add chapter `Installation`.
Merge pull request #22 from htgoebel/master

Add chapter `Getting Started`.
Add documentation for debops.slapd
Merge pull request #24 from drybjed/debops-slapd

Add documentation for debops.slapd
Add notice about DebOps examples to "getting started" page.
Change some headings in "getting started" page.
Add project description to documentation main page.

This text is taken from the projects home-page.
Add contributions page.

This page was shamelessly taken from
<https://github.com/debops/debops/blob/master/CONTRIBUTING.rst>