Update README
git trigger -> git deploy in README
Link to Salt
Link to wikitech in README
Roll-up commit from Wikimedia's repo

* Deployment module changes for trebuchet-trigger
* Code documentation for trebuchet's deployment module
* Add Sphinx function documentation for deploy module
* Ensure submodules are checked out on the deployment server
* Continue on single repo failures for deployment server init
* Fix submodule fetching in trebuchet