Pull idmapping documentation updates from Christian Brauner:
 "The bulk of the idmapped work this cycle was adding support for
  idmapped mounts to btrfs.

  While this required the addition of a (simple) new vfs helper all the
  work is going through David Sterba's btrfs tree. It was way simpler to
  do it this way rather then forcing David to coordinate between his
  btrfs and my tree. Plus I don't care who merges it as long as I feel I
  can trust the maintainer and the btrfs folks were really fast and
  helpful in reviewing this work.

  As always, associated with the btrfs port for idmapped mounts is a new
  fstests extension specifically concerned with btrfs ioctls (e.g.
  subvolume creation, deletion etc.) on idmapped mounts which can be
  found in the fstests repo as 5f8179ce8b00 ("btrfs: introduce btrfs
  specific idmapped mounts tests").

  Consequently, this cycle the idmapping pull is boring. It only
  contains documentation updates, specifically about how idmappings and
  idmapped mounts work"

* tag 'fs.idmapped.v5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  doc: give a more thorough id handling explanation