Add Documentation section to README
Add Documentation section to README

Make it more obvious that we have code documentation easily accessible
online.

Change-Id: Iafe79c8e7a5edfce43c317148736118ea4591b8c
Reviewed-on: http://gerrit.causes.com/45709
Tested-by: jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@brigade.com>
Reviewed-by: Shane da Silva <67fb7bfe39f841b16a1f86d3928acc568d12c716@brigade.com>

mzp/haml-lint,skateman/haml-lint