update README to be more approachable
update README to be more approachable

Polymer/tools,Polymer/tools,bendroid/vulcanize,Polymer/tools,threeday0905/vulcanize,Polymer/tools,wprl/spock,rcorp/vulcanize,rcorp/vulcanize,Polymer/polymer-bundler,bendroid/vulcanize,Polymer/polymer-bundler,threeday0905/vulcanize,Polymer/polymer-bundler