Improve Admin UI Readme

It's first time a try to start up the development environment and, following the readme instructions, it is very confusing. These steps/instructions should be reviewed and improved in a way anyone can start developing easily.

Some problems I've found:

• Bower is already a requisite, no need of installing it again. (https://github.com/aerogear/aerogear-unifiedpush-server/blame/master/admin-ui/README.md#L12)
• Running this gives an error, there are more steps that have to be done before doing the grunt command (https://github.com/aerogear/aerogear-unifiedpush-server/blame/master/admin-ui/README.md#L19)
• No idea what "properly" stands for here (https://github.com/aerogear/aerogear-unifiedpush-server/blame/master/admin-ui/README.md#L23)
• This route does not exists, it can be guessed it means the admin-ui folder path however (https://github.com/aerogear/aerogear-unifiedpush-server/blame/master/admin-ui/README.md#L26)

And some "error" section would be fine as well, I got this error however I have everything "properly" set:

$ grunt initLocalConfig
>> Local Npm module "grunt-cli" not found. Is it installed?

Running "initLocalConfig" task
Fatal error: jbossweb directory /home/jgallaso/projects/eap-6.4/standalone/deployments/ag-push.war configured in ./local-config.json is not directory (must be exploded WAR)