Add some extra detail to the intro

Author: eholk

docs/code-quality/c6059.md

@@ -14,6 +14,8 @@ ms.assetid: 343a4cd1-048a-4edf-bb4b-187097bb6093
 
 This warning indicates that a call to a string concatenation function is probably passing an incorrect value for the number of characters to concatenate. This defect might cause an exploitable buffer overrun or crash. A common cause of this defect is passing the buffer size (instead of the remaining number of characters in the buffer) to the string manipulation function.
 
+This warning helps identify the common error of sending the size of the target buffer instead of the size of the data. It does so by detecting when the size used to allocate the buffer is passed, unchanged, to the function putting data in the buffer.
+
 Code analysis name: `BAD_CONCATENATION`
 
 ## Example