Added documentation to example site_make config.

	modified:   site_make.example.yml
Added drush_print to give visibility when -v is not used.

	modified:   site_make.drush.inc
Changed workflow.

  Move subtree add/pull up so we can keep the git history clean and easy to
  understand.

	modified:   site_make.drush.inc
Updated logic. Tidy commit history. Simplify subtree functions.

	modified:   site_make.drush.inc
	modified:   site_make.example.yml
Changed logic. Execute subtree commands first, then the rest.

  This way, info loaded from make files includes stuff from subtrees with make
  files that have updates pulled in.

	modified:   site_make.drush.inc
README.md