Set required ruby version
Made the usage of repositories more clear.

In order to prevent a wrong setup of the repositories a small code
example was added to the README.md.
Added proper includes to the README.md.
Merge pull request #29 from joneslee85/patch-1

Set required ruby version
Merge pull request #30 from Partyschaum/repository_explanation

Made the usage of repositories more clear.
[ci skip] Document the usage of #first in EXAMPLE.md. Ref #31
Syntax highlighting for Gemfile instruction

[ci skip]
Merge pull request #37 from parndt/patch-1

Syntax highlighting for Gemfile instruction