More info in Readme

[dlapiduz]

Can you add more information about how the agent is supposed to work in the Readme?

[nyetsche]

Also, build instructions? A naive 'gem build *.gemspec" fails for me:

Invalid gemspec in [codedeploy_agent-1.1.0.gemspec]: uninitialized constant Gem::Specification::FileList
ERROR:  Error loading gemspec. Aborting

[surybala]

We've recently refreshed the repo and added instructions to build and run tests. Resolving.