add details about running bosh create release

As someone new to bosh/cf/etc, I was confused when I ran into errors running bosh create release.

I did not know 

* I had to run the command in the cf-release directory
* I needed to run the update script in cf-release first, to pull in the submodules
* The release name I was prompted to enter needed to match the one in the deployment.yml file

I added this information to the top-level README.