README: add note on how to send a patch series with cover-letter
README: add note on how to send a patch series with cover-letter

As patch series should include a cover letter describing the whole
series shortly add a note on this in the README.

Signed-off-by: Richard Leitner <0f2fdd4d2dfbb4dde6236fd550af0a2071b34781@skidata.com>
Signed-off-by: Maxin B. John <4470e5a3cfbc7ff75506df1ae89969a0d8cce1df@intel.com>

rehsack/meta-java,rehsack/meta-java,rehsack/meta-java,rehsack/meta-java,rehsack/meta-java