License concerns when embedding script in busybox binary

[Kang-Che Sung]

Since we are introducing the feature of embedding scripts into BusyBox, and
user may now include and build their custom scripts into the BusyBox binary, I
think there's one thing we forgot to address when this binary would be
distributed. That is: the license problem.

Specifically, I think the current state of config ASH_EMBEDDED_SCRIPTS help
text did not yet warn builders that the binary may be distributed **only when
the embedding scripts are GPLv2-compatible**. Builder and distributors may
accidentally violate copyright if they didn't get careful at reading the
BusyBox licenses. I think something should be done to make the warning more
explicit.

I'm not sure if additional measures needs to be done to check the script's
license (is it good to require every script in the embed directory to carry a
licence tag, or is that overkill?)