Add a better explanation about how to deal with user modules

  ifeq ($(filter $(GRANDFATHERED_USER_MODULES),$(LOCAL_MODULE)),)

    $(warning *** Module name: $(LOCAL_MODULE))

    $(warning *** Makefile location: $(LOCAL_PATH))

    $(warning * )

    $(warning * Each module must use a LOCAL_MODULE_TAGS in its)

    $(warning * Android.mk. Possible tags declared by a module:)

    $(warning * )

    $(warning *     optional, debug, eng, tests, samples)

    $(warning * )

    $(warning * If the module is expected to be in all builds)

    $(warning * of a product, then it should use the)

    $(warning * "optional" tag: )

    $(warning * )

    $(warning *    Add "LOCAL_MODULE_TAGS := optional" in the)

    $(warning *    Android.mk for the affected module, and add)

    $(warning *    the LOCAL_MODULE value for that component)

    $(warning *    into the PRODUCT_PACKAGES section of product)

    $(warning *    makefile(s) where it's necessary, if)

    $(warning *    appropriate.)

    $(warning * )

    $(warning * If the component should be in EVERY build of ALL)

    $(warning * products, then add its LOCAL_MODULE value to the)

    $(warning * PRODUCT_PACKAGES section of)

    $(warning * build/target/product/core.mk)

    $(warning * )

    $(error user tag detected on new module - user tags are only supported on legacy modules)

  endif

endif