Documentation/kbuild: Document gendwarfksyms build dependencies

Documentation/kbuild: Document gendwarfksyms build dependencies

Although dependencies for gendwarfksyms were recently added to the
packaging rules [1-2], the corresponding documentation was missing.

Document the required build dependencies for gendwarfksyms, and
include a few examples for installing these dependencies on some
distributions.

[1] commit 657f96cb7c06 ("kbuild: deb-pkg: Add libdw-dev:native to Build-Depends-Arch")
[2] commit 5bd6bdd0f76e ("kbuild: rpm-pkg: Add (elfutils-devel or libdw-devel) to BuildRequires")

Signed-off-by: Jihan LIN <linjh22s@gmail.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Link: https://patch.msgid.link/20260114-documents_gendwarfksyms-v2-1-297c98bd62c6@gmail.com
[nathan: Applied Petr's suggested changes from review and minor commit
         message formatting adjustments]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>