Update winrepo documentation

Added in documentation about how full_name and versions are used when verifying installed packages and how to find this information. Added link to init.sls examples.  Updated the information about package upgrades not being supported (now works in the latest version). Updated the 7zip example because it didn't verify correctly when running highstate.
Merge pull request #6254 from Crazybus/patch-1

Update winrepo documentation