Clarify documentation about dev server daemon mode
Clarify documentation about dev server daemon mode

This is to resolve issue #105.
ArseniKavalchuk/gradle-appengine-plugin,MGronber/gradle-appengine-plugin,judeebene/gradle-appengine-plugin,GoogleCloudPlatform/gradle-appengine-plugin,loosebazooka/gradle-appengine-plugin,mpoehler/gradle-appengine-plugin