Add some comments to a Kconfig file

arch/sim/Kconfig

@@ -41,6 +41,12 @@ config SIM_CYGWIN_DECORATED
 		underscore to the beginning of the symbol name.  Newer versions of
 		Cygwin do not seem to do this.
 
+		How do you know if you need this option?  You could look at the generated
+		symbol tables to see if there are underscore characters at the beginning
+		of the symbol names.  Or, if you need this option, the simulation will not
+		run:  It will crash early, probably in some function due to the failure to
+		allocate memory.
+
 choice
 	prompt "X64_64 ABI"
 	default SIM_X8664_SYSTEMV if HOST_LINUX