Add additional readme files for all produced images (#141)

scheduler/README.md

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+# Kopano Scheduler image
+
+[![](https://images.microbadger.com/badges/image/zokradonh/kopano_scheduler.svg)](https://microbadger.com/images/zokradonh/kopano_scheduler "Microbadger size/labels") [![](https://images.microbadger.com/badges/version/zokradonh/kopano_scheduler.svg)](https://microbadger.com/images/zokradonh/kopano_scheduler "Microbadger version")
+
+Service to carry out repeating tasks within the Kopano environment. Takes care of initial user sync on startup and creating the public store.
+
+## Recurring tasks and maintenance tasks within Kopano
+
+There are certain tasks within Kopano that either need to be executed once (like creating the public store when starting a new environment for the first time) or on a regular base (like syncing the internal user list with and external ldap tree). For convinience this project includes a "scheduler" container that will take care of this and that can be dynamically configured through env variables.
+
+The container knows two kinds of cron jobs (the crontab syntax is used for actual jobs):
+
+- `CRON_ZPUSHGAB=0 22 * * * docker exec kopano_zpush z-push-gabsync -a sync`
+  - Jobs prefixed with `CRON_` are executed once at container startup (and container startup will fail if one of the jobs fail) and then at the scheduled time.
+- `CRONDELAYED_KBACKUP=30 1 * * * docker run --rm -it zokradonh/kopano_utils kopano-backup -h`
+  - Jobs prefixed with `CRONDELAYED_` are only executed at the scheduled time.
+
+Instead of using the internal scheduler one can also just use an existing scheduler (cron on the docker host for example) to execute these tasks.