DOCSP-44801: Client-side projection breaking v3.0 breaking change (mongodb#321)

Author: mcmorisi

source/upgrade/v3.txt

@@ -98,6 +98,14 @@ Version 3.0 Breaking Changes
 
 - The LINQ2 provider has been removed from this version of the driver.
   You must use LINQ3 for all LINQ queries.
+  
+  Queries that use client-side projections will throw an ``ExpressionNotSupportedException``
+  error by default. To enable client-side projections, set the
+  ``EnableClientSideProjections`` property of a ``TranslationOptions`` object to
+  ``true``. You can pass this ``TranslationOptions`` object to an
+  ``AggregateOptions`` or ``FindOptions`` object to enable client-side projections
+  for a single query, or to a ``MongoClientSettings`` object to enable client-side projections
+  for all queries in an application.
 
 - Previous versions of the {+driver-short+} supported two GUID representation modes.
   In version 3.0, ``GuidRepresentationMode.V3`` is the only supported mode. This change