Create installing_apps.rst

I suggest to amend the documentation and add the following to the apps.owncloud.com website as well. Since this is a new section and describes issues under active discussion I am putting this up as a partial solution to https://github.com/owncloud/documentation/issues/473 inviting comments and corrections as well as instructions from the maintainers as to where exactly this might be placed in the documentation.
You can add an issue tracker to your apps page. It doesnt matter where you ask your noob questions, the dev gets notified anyways, the comment section makes it just really hard to discuss this. So no, issue tracker (it has issue in its name, thats the way to go) if not available then comment section