Remove duplicated inclusion of `rspec-system-puppet` helpers.

The helpers are already included a couple of lines above the deleted line, and
including them inside the `RSpec.configure` block argument would have no effect
anyway.
Simplify introductory documentation.

As a newcomer, I'd like to see just the minimum amount of work required to use
the library. Additional examples and enhancements should be put in a different
paragraph, if pertinent.
Release 2.2.1

Updates CHANGELOG and gemspec for a new release.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge branch 'release_221'

* release_221:
  Release 2.2.1
Merge pull request #20 from stefanozanella/simplify_readme

Simplify introductory documentation.
Provide ability to test against rspec-system git or file based paths

Signed-off-by: Ken Barber <ken@bob.sh>
Added option to skip files when copying modules
and skip .rspec_system by default
execute must return a result
Added documentation for :skip option
Merge pull request #26 from tbartelmess/master

Added option to skip files when copying modules
Merge pull request #24 from kbarber/test_against_rspec_system_master

Provide ability to test against rspec-system git or file based paths
Merge pull request #19 from stefanozanella/update_docs

Remove duplicated inclusion of `rspec-system-puppet` helpers.
Allow running puppet apply as a non root user
Merge pull request #27 from maestrodev/run-as-user

Allow running puppet apply as a non root user
Add support for --write-catalog-summary option to apply