Adding SELinux users and roles section

Added section on SELinux users and roles
Included flag to check via ls or ps command (or others)
Included link resource to SELinux documentation
Reset list tags and removed whitespace

Change-Id: Ic7009d3f3a3ca8dfa16478ab53741d5ddb309657
Closes-Bug: #1343583
Merge "Adding SELinux users and roles section"