Document new parameter in README

Author: adamtheturtle

README.rst

@@ -182,9 +182,8 @@ Matching deleted targets
 
 Matching a target which has been deleted returns a 500 (INTERNAL SERVER ERROR) response within the first few seconds.
 This timeframe is not consistent on the real Vuforia Web Services.
-On the mock, this timeframe is always three seconds.
-
-TODO explain option here
+On the mock, this timeframe is three seconds by default.
+``MockVWS`` takes a parameter ``query_recognizes_deletion_seconds`` to change this.
 
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