document new // separator in omero.fs.repo.path

reflects changes arising from fixing
http://trac.openmicroscopy.org.uk/ome/ticket/12160
adjust for permitting no root-owned directories
emphasize user ownership in bold
Merge pull request #783 from mtbc/rebased/develop/template-path-ownership

document new // separator in omero.fs.repo.path (rebased from dev_5_0)