Update MSVC flags descriptions

Closes cpp-best-practices#79

Author: lefticus

02-Use_the_Tools_Available.md

@@ -115,7 +115,7 @@ Consider using `-Weverything` and disabling the few warnings you need to on Clan
 
 `/permissive-` - [Enforces standards conformance](https://docs.microsoft.com/en-us/cpp/build/reference/permissive-standards-conformance).
 
-`/W4 /W44640` - use these and consider the following
+`/W4 /W14640` - use these and consider the following (see descriptions below)
 
  * `/W4` All reasonable warnings
  * `/w14242` 'identfier': conversion from 'type1' to 'type1', possible loss of data