[MIPS] Kconfig: Clarify description of CROSSCOMPILE.

Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig.debug

@@ -6,7 +6,13 @@ config CROSSCOMPILE
 	bool "Are you using a crosscompiler"
 	help
 	  Say Y here if you are compiling the kernel on a different
-	  architecture than the one it is intended to run on.
+	  architecture than the one it is intended to run on.  This is just a
+	  convenience option which will select the appropriate value for
+	  the CROSS_COMPILE make variable which otherwise has to be passed on
+	  the command line from mips-linux-, mipsel-linux-, mips64-linux- and
+	  mips64el-linux- as appropriate for a particular kernel configuration.
+	  You will have to pass the value for CROSS_COMPILE manually if the
+	  name prefix for your tools is different.
 
 config CMDLINE
 	string "Default kernel command string"