USERGUIDE: replace PostmarketOS with postmarketOS

Branding for postmarketOS denotes the correct capitalization
Added info on crond - took me a while to figure out why sxmo_rtcwake.sh did not work

Signed-off-by: Anjandev Momi <anjan@momi.ca>
Remove typo
Move SXMO_THRESHOLD entry bellow the LISGD one
Update the userscript part with the new file system
Update note about lock screen to fix dead link & fix oudated info on images
Remove outdated changelog & generator script

Reading ML for each version and git log is more useful - also we no longer
track images / done through postmarketos so manging this script / images based
changelog doesn't make sense anymore.
In example xinit unset SXMO_LOCK_SCREEN_OFF=1 and add note in screenlock doc
Fix the cronjob entry
documented changes in rtcwake and some other minor changes in recent patches

Signed-off-by: Stacy Harper <contact@stacyharper.net>
in 'USERGUIDE.md': updated reference to 'sxmo_gestures.sh' to the current 'sxmo_inputhandler.sh' within 'user customizable functionality' section, and updated reference to 'hooks/gestures' to 'hooks/inputhandler' in same paragraph.

Signed-off-by: Maarten van Gompel <proycon@anaproy.nl>
various language fixes and minor enhancements in the documentation after the last batch of commits
Add a part about sxmo_migrate.sh
Update some of the env variable
Update international numbers part including the deduplication fixes
Add a note about the new contact appmenu entry
Update somethings about incoming calls
Add a note about the contextual appmenu to reply or call the number
Update the doc after the cron job screenlock changes.