Added an explanation at the top for users who find this dev manual, to go directly to the user manual. Added the user manual as an explict link at the bottom so developers have it on their mind. :) Changed the very top sentence about Kotti to have the word nimble instead of the phrase light-weight.
Fixed links to user manual on index page. Reworked the section of the developer manual on contributing to have sections for contributing to code, dev manual, and user manual.
Changed the pip install instructions to use master, with a note added about how to find and use a tagged version.
Added a link to PyPI in the installation instructions, for finding the latest Kotti release.
Merge pull request #207 from geojeff/user_manual_link

User manual link
Fix wrong spelling of permission.
Added some tests to check that Content is also extensible with a workflow.