added more documentation for frequent snapshots

README.md

@@ -26,6 +26,7 @@ And its /etc/sanoid/sanoid.conf might look something like this:
 #############################
 
 [template_production]
+        frequently = 0
         hourly = 36
         daily = 30
         monthly = 3

sanoid.defaults.conf

@@ -16,8 +16,16 @@ recursive =
 use_template =
 process_children_only =
 
-# The period in minutes for frequent snapshots,
-# should be in the range of 1-30 and divide an hour without remainder
+# for snapshots shorter than one hour, the period duration must be defined
+# in minutes. Because they are executed within a full hour, the selected
+# value should divide 60 minutes without remainder so taken snapshots
+# are apart in equal intervals. Values larger than 59 aren't practical
+# as only one snapshot will be taken on each full hour in this case.
+# examples:
+# frequent_period = 15 -> four snapshot each hour 15 minutes apart
+# frequent_period = 5 -> twelve snapshots each hour 5 minutes apart
+# frequent_period = 45 -> two snapshots each hour with different time gaps
+# between them: 45 minutes and 15 minutes in this case
 frequent_period = 15
 
 # If any snapshot type is set to 0, we will not take snapshots for it - and will immediately