Update installation.rst

Updated installation instructions to provide additional detail and clarity re: cloning the oh-mainline repository and running the OpenHatch's web server on a local computer
Merge pull request #156 from shaunagm/master

improved documentation.rst, added files from prev commit to index.rst to...
Merge pull request #157 from willingc/master

Update installation.rst
Merge branch 'master' of github.com:openhatch/oh-mainline