Add instructions about how to add a toy.

Change-Id: I8080db4f2d205760880cece72c21a0dd32ec1c78
diff --git a/Android.mk b/Android.mk
index 2f602f6..5e08afe 100644
--- a/Android.mk
+++ b/Android.mk
@@ -33,6 +33,17 @@
 #  git commit -a
 
 
+#
+# To add a toy:
+#
+
+#  make menuconfig
+#  # (Select the toy you want to add.)
+#  make clean && make  # Regenerate the generated files.
+#  # Edit LOCAL_SRC_FILES below to add the toy.
+#  # If you just want to use it as "toybox x" rather than "x", you can stop now.
+#  # If you want this toy to have a symbolic link in /system/bin, add the toy to ALL_TOOLS.
+
 include $(CLEAR_VARS)
 
 LOCAL_SRC_FILES := \