Update PULL_REQUEST_TEMPLATE.md
Update PULL_REQUEST_TEMPLATE.md

* Fixes an old link
* Adds some default whitespace at beginning
* Formats instructions as list
* Tells user to delete said instructions.
ewiseblatt/spinnaker,skim1420/spinnaker,duftler/spinnaker,spinnaker/spinnaker,skim1420/spinnaker,ewiseblatt/spinnaker,ewiseblatt/spinnaker,spinnaker/spinnaker,duftler/spinnaker,spinnaker/spinnaker,duftler/spinnaker,skim1420/spinnaker,ewiseblatt/spinnaker,spinnaker/spinnaker,skim1420/spinnaker,duftler/spinnaker