DOCSP-27763 Update convention factor default value (#2480)

* Update convention factor default value

* Chris feedback

Author: jordan-smith721

source/core/queryable-encryption/reference/limitations.txt

@@ -25,8 +25,9 @@ Contention Factor
 Contention factor is a setting that helps tune performance based on the
 number of concurrent connections.
 
-Contention factor is immutable, and can only be set when specifying a
-field for encryption. The default value is ``0``.
+You can set the contention factor only when specifying the field for encryption.
+Once you specify a field for encryption, the contention factor is immutable. If
+you don't specify the contention factor, it uses the default value of ``4``.
 
 Manual Data Key Creation
 ++++++++++++++++++++++++