Add howto on data sharing

[fosterrath-mila]

The sharing data section in the policy section is very limited.
There is a need for new users to have a practical section on HOW to share data.

Write up a practical guide giving examples to attain data sharing goals.

[vict0rsch]

To expand a little I think it should cover (at least, feel free to add 🙂)

• projects
  • group creation request to it-support
  • profs approve
  • provide usernames
  • how to use ACLs (or anything else)
  • things like chgrp -R <group> <folder> if need be
  • or umask?
  • This is all far from my expertise 😅
• scratch
  • make a $SCRATCH/Public folder
  • create subdirs
  • chmod recursively with the appropriate permissions

[btravouillon]

Closed by #121.