[MTD] mtdoops: Document usage in Kconfig

Add usage instructions to Kconfig for mtdoops driver.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
diff --git a/drivers/mtd/Kconfig b/drivers/mtd/Kconfig
index 8848e8a..661eac0 100644
--- a/drivers/mtd/Kconfig
+++ b/drivers/mtd/Kconfig
@@ -286,6 +286,9 @@
 	  buffer in a flash partition where it can be read back at some
 	  later point.
 
+	  To use, add console=ttyMTDx to the kernel command line,
+	  where x is the MTD device number to use.
+
 source "drivers/mtd/chips/Kconfig"
 
 source "drivers/mtd/maps/Kconfig"