Add vulcanize to install steps.
Documented that this.$ only contains static nodes. Fixes #460.

Added mention of using querySelector from a known node
in the shadow to find other nodes.
Fix indentation
Updated to address comments.
Merge branch 'master' of https://github.com/Polymer/docs into docs-460
Moved note up to make it more prominent and rephrased opening paragraph to remove misleading phrase, 'Every node...'. Also escaped mustaches in code example.
Clarified intro sentence, made capitalization consistent for shadow DOM.
Merge pull request #562 from arthurevans/docs-460

Add note that this.$ only contains static IDs (not databound nodes).