docs for repo hosters

[ThomasWaldmann]

maybe it would be nice to have a section especially for mass hosters (== everybody who hosts a big amount of borg repos, potentially for other people).

stuff like:

• how to name borg binaries (like e.g. borg-1.2.3rc1)
• how users can select some borg version
• performance optimisations, like:
  • no self test
  • borg fat binary: use dir-mode .tgz, not single-file-mode .exe
• borg 1.2: run borg compact server side and do hoster controlled scheduling to better distribute CPU / memory and I/O load
• ...