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.
Ok, in that case it would be great to add to teh documentation that its easier to handle issues that are raised directly on github. 

Questions: would you say most developers who have apps there whoud agree? Would you say there is a genuine usecase for the comment section beyond a fallback in case there is no issue tracker or is it just annoying and obsolete in its current state? Is there anything that should be improved about it? I m asking cos I do think that the current system and its frequent cross referrals are a confusing bottleneck for new users.