Also update build from source instructions

We support multiple versions of the CIS benchmark

There was an extra '\' sign in the docker pull command

Updates to travis file, readme and help text

Simply clone the project, compile the go app and run ./cis_kubernetes

* Replace the default help text

* Readme file, including the test config format documentation

* Typo

* Warn if config files / executables aren't found

* Ignore original name of executable (as per current README)

* Update tests to avoid failing on stat of a non-existant file

* Add a makefile for ease of build