Renamed crontab templates files to be template.* rather than *.template.
This is an 'optimize for lazy' tweak, since if we use a prefix, then
the actual crontab files named of the form crontab.$USER.${HOSTNAME%%.*}
won't have command line completion conficts with the templates.
Added a ReadMe.md file describing the suggested (and with HMS required)
naming convention for crontab files.
Added a command summary doc for the sdp_sync.sh script that manages
crontab files in a tight ship deployment. The reference to this file
from the ReadMe.md file won't work now with this change in the dev branch,
but will work once promoted to main.