[PATCH RFC] Overlayfs mode support

This dramatical reduce startup time on ssd and hdd,
created for prevent useless copy browser data from ssd to tmpfs

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
Fix typo

Signed-off-by: Timofey Titovets <nefelim4ag@gmail.com>
cosmetic updates for overlayfs
Merge branch 'Nefelim4ag-master' into unstable
update manpage to overlayfs
minor tweak to /etc/psd.conf
clearer wording in /etc/psd.conf
minor cosmetic tweaks
update to manpage
additional tweaks to wording of manpage and config
add overlayfs use per profile
fix typo in var
fix typo
Add Documentation for NixOS