Fix development instructions.

* Added etcd installation instructions ptr
  (cannot run integ tests w/o it).

* Removed unnecessary mercurial instructions
  (install works w/o mercurial).

* Moved pre-commit hook installation instructions from development
  loop to git clone section (it's a one time setup).

* Ditto for "setting upstream remote to no_push".

* Gathered Go install/upgrade discussion to one section.

* Put build/test instructions between checkout and commit.

  Formerly, build was up before fork (odd), and test was
	tacked at end of doc.

* Brought text into sync with the Workflow fig:

  * Assured 1:1 correspondence between numbered figure steps
    and numbered section headers - had no numbers before.

  * Used "$working_dir", "$user" and "myfeature" in text to
    match figure.