Update conf/storage-schemas.conf.example

Note about resolution and aggregation with example

conf/storage-schemas.conf.example

@@ -1,9 +1,19 @@
 # Schema definitions for Whisper files. Entries are scanned in order,
 # and first match wins. This file is scanned for changes every 60 seconds.
 #
-#  [name]
-#  pattern = regex
-#  retentions = timePerPoint:timeToStore, timePerPoint:timeToStore, ...
+# Definition Syntax:
+#
+#    [name]
+#    pattern = regex
+#    retentions = timePerPoint:timeToStore, timePerPoint:timeToStore, ...
+#
+# Remember: To support accurate aggregation from higher to lower resolution
+#           archives, the precision of a longer retention archive must be
+#           cleanly divisible by precision of next lower retention archive.
+#
+#           Valid:    60s:7d,300s:30d (300/60 = 5)
+#           Invalid:  180s:7d,300s:30d (300/180 = 3.333)
+#
 
 # Carbon's internal metrics. This entry should match what is specified in
 # CARBON_METRIC_PREFIX and CARBON_METRIC_INTERVAL settings