updated upgrading information

Documentation/Books/Users/NewFeatures/NewFeatures23.mdpp

@@ -40,7 +40,7 @@ in the future.
 
 !SUBSUBSECTION Alternative operator syntax
 
-ArangoDB 2.3 allows to write the use the following alternative forms for the 
+ArangoDB 2.3 allows to use the following alternative forms for the 
 logical operators:
 - `AND`: logical and
 - `OR`: logical or
@@ -300,4 +300,4 @@ Jobs can be scheduled in advance or set to be executed immediately, the number o
 
 The request and response objects in Foxx controllers now provide methods for reading and writing raw cookies and signed cookies.
 
-Mounted Foxx apps will now be loaded when arangod starts rather than at the first database request. This may result in slightly slower start up times (but a faster response for the first request).
+Mounted Foxx apps will now be loaded when arangod starts rather than at the first database request. This may result in slightly slower start up times (but a faster response for the first request).

Documentation/Books/Users/Upgrading/UpgradingChanges23.mdpp

@@ -310,3 +310,17 @@ warnings will eventually disappear.
 
 The HTTP REST API method at `POST /_admin/modules/flush` has been removed. 
 
+
+!SECTION Known issues
+
+In ArangoDB 2.3.0, AQL queries containing filter conditions with an IN expression 
+will not yet use an index:
+
+    FOR doc IN collection FILTER doc.indexedAttribute IN [ ... ] RETURN doc
+  
+    FOR doc IN collection
+      FILTER doc.indexedAttribute IN [ ... ]
+      RETURN doc
+
+We’re currently working on getting the IN optimizations done, and will ship them in 
+a 2.3 maintenance release soon (e.g. 2.3.1 or 2.3.2).