adding NICE and NICE_VAL and ability to override backup numbers in config

default-docker-compose.conf-sample

@@ -17,3 +17,18 @@ DUMP_CMD='pg_dumpall -c -U postgres'
 # email address to send reports to, and subject
 EMAIL=webmaster@oerfoundation.org
 EMAIL_SUBJ="Mastodon on OERu Open Postgres Backup Report"
+#
+# Optional overrides
+#
+# Default retention
+#BU_TO_KEEP_HOURLY=24
+#BU_TO_KEEP_DAILY=7
+#BU_TO_KEEP_WEEKLY=4
+#BU_TO_KEEP_MONTHLY=12
+#BU_TO_KEEP_YEARLY=7
+#
+# Set backup priority: -20 highest, 0 default, 19 lowest
+#NICE_VAL=0
+#
+# Verbosity 0 = false, 1 = true
+#VERBOSE=0