Added documentation on running debuginfod server and using it on the target.
Added the term DEBUGINFOD_URLS definition in ref-manual/variables.rst
(From yocto-docs rev: a16ae140e26482c81ce733f20f8c68c6eba55f35)
Signed-off-by: Dorinda Bassey <dorindabassey@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>