The override format in a comment is incorrect, fix it.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
# To use linux-yocto-custom in your layer, copy this recipe (optionally
# rename it as well) and modify it appropriately for your machine. i.e.:
#
-# COMPATIBLE_MACHINE_yourmachine = "yourmachine"
+# COMPATIBLE_MACHINE:yourmachine = "yourmachine"
#
# You must also provide a Linux kernel configuration. The most direct
# method is to copy your .config to files/defconfig in your layer,