Add form example to style guide
Add form example to style guide

* Indicates how default legend and fieldset styles create a layout that
separates headings from content

robinwhittleton/whitehall,robinwhittleton/whitehall,YOTOV-LIMITED/whitehall,robinwhittleton/whitehall,hotvulcan/whitehall,hotvulcan/whitehall,hotvulcan/whitehall,ggoral/whitehall,robinwhittleton/whitehall,ggoral/whitehall,alphagov/whitehall,askl56/whitehall,hotvulcan/whitehall,alphagov/whitehall,alphagov/whitehall,alphagov/whitehall,ggoral/whitehall,YOTOV-LIMITED/whitehall,ggoral/whitehall,askl56/whitehall,askl56/whitehall,askl56/whitehall,YOTOV-LIMITED/whitehall,YOTOV-LIMITED/whitehall