Updated the description to tell the user they can safely
clean up the DL_DIR after creating tarballs of the source
files from downloaded repos.
(From yocto-docs rev: 6aff69632ea3102b6389ea510e1e3fa5bf1c2123)
Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>