Documents the time series collection index creation. (#5682) (#5737)

* Add info about time series collection auto-index creation

* replace with links

* better linking

* how about a link that is formatted correctly?

* review suggestion

Author: MongoCaleb

source/core/timeseries-collections.txt

@@ -111,11 +111,13 @@ and query your data as you normally would.
 MongoDB treats time series collections as writable non-materialized
 :ref:`views <views-landing-page>` backed by an internal collection. When
 you insert data, the internal collection automatically organizes time
-series data into an optimized storage format.
+series data into an optimized storage format. 
 
-When you query time series collections, you operate on one document per
-measurement. Queries on time series collections take advantage of the
-optimized internal storage format and return results faster.
+Since MongoDB 6.3, when you create a new time series collection, MongodDB 
+generates a :ref:`compound index <index-create-compound>` on the 
+:ref:`metaField and timeField <time-series-fields>` fields. Queries on time 
+series collections take advantage of this index, as well as the optimized 
+storage format, to improve query performance.
 
 .. tip::
 

source/release-notes/6.3.txt

@@ -210,6 +210,13 @@ MongoDB 6.3 adds the following :ref:`time series parameters
 Starting in MongoDB 6.3, the :dbcommand:`compact` command works with
 :ref:`time series collections <manual-timeseries-landing>`.
 
+Time Series Indexing
+--------------------
+
+Starting in MongoDB 6.3, MongoDB automatically generates a compound 
+index on the ``metaField`` and ``timeField`` fields when the collection is 
+created.
+
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