[DOCS] Drafted overview of calendars and special events (elastic/x-pack-elasticsearch#3395)

Original commit: elastic/x-pack-elasticsearch@970cfea67e

docs/en/ml/calendars.asciidoc

@@ -0,0 +1,28 @@
+[[ml-calendars]]
+=== Calendars and Scheduled Events
+
+Sometimes there are periods when you expect unusual activity to take place,
+such as bank holidays, "Black Friday", or planned system outages. If you
+identify these events in advance, no anomalies are generated during that period.
+The {ml} model is not ill-affected and you do not receive spurious results.
+
+You can create calendars and scheduled events in the **Settings** pane on the
+**Machine Learning** page in {kib} or by using {ref}/ml-apis.html[{ml} APIs].
+
+A scheduled event must have a start time, end time, and description. You can
+identify zero or more scheduled events in a calendar. Jobs can then subscribe to
+calendars and the {ml} analytics handle all subsequent scheduled events
+appropriately.
+
+If you want to add multiple scheduled events at once, you can import an
+iCalendar (`.ics`) file in {kib} or a JSON file in the
+//{ref}/ml-post-calendar-event.html[
+add events to calendar API
+//]
+.
+
+NOTE: Bucket results are generated during scheduled events but they have an
+anomaly score of zero. For more information about bucket results, see
+{ref}/ml-results-resource.html[Results Resources].
+
+//TO-DO: Add screenshot showing special events in Single Metric Viewer?

docs/en/ml/overview.asciidoc

@@ -3,6 +3,7 @@
 
 include::analyzing.asciidoc[]
 include::forecasting.asciidoc[]
+include::calendars.asciidoc[]
 
 [[ml-concepts]]
 === Basic Machine Learning Terms