Prominently mention SD is created from first <template>

[ebidel]

There's mention here:
http://www.polymer-project.org/polymer.html#createlightdom

But it should also be:
http://www.polymer-project.org/polymer.html#element-declaration

Also mention not to use repeat or other binding attributes on this <template>

[robdodson]

Looks related to this as well Polymer/polymer#245

[ebidel]

This is also prominent in @arthurevans's data binding update. Closing this issue.