update readme: don't have to install grunt-karma

The generator installs grunt-karma for you unless you tell it not to: https://github.com/yeoman/generator-karma/blob/42aa8015e4862cff874d943dedc9c068ba2ab2b7/lib/generators/app/index.js#L21

also: make AngularJS generator link more specific.
Merge pull request #39 from X1011/master

update readme: don't have to install grunt-karma