Allow short-specs

* Clarify the template to describe the requirements and process for
  submitting initial drafts better.
* Add testing for a specs/backlog dir which allows "short specs"
  to be accepted in that dir even if they are missing some sections.
* Add a sample file to the specs/backlog dir, for demonstration.
* Update the index page

Change-Id: I634635467f5cbe565958dbcd360399bc5f0b96ec
Merge "Allow short-specs"