Marketplace version updates

Hey Jim - here are a few updates for the Marketplace documentation to conform to newly established publishing policies for the Marketplace.  I elected to issue the pull request to your 6.1.x branch, as this applies there (and I hope it can be pushed to liferay.com/documentation soon).  I'm not sure if I also have to submit this to your master branch so that it is also included in the 6.2 docs?