docs: submitting-patches: clarify that signers may use their discretion on tags

Tags are really appreciated by maintainers in general, since it means
someone is willing to put their name on a commit, be it as a reviewer,
tester, etc.

However, signers (i.e. submitters carrying tags from previous versions
and maintainers applying patches) may need to take or drop tags, on a
case-by-case basis, for different reasons.

Yet this is not explicitly spelled out in the documentation, thus there
may be instances [1] where contributors may feel unwelcome.

Thus, to clarify, state this clearly.

Link: https://lore.kernel.org/rust-for-linux/CAEg-Je-h4NitWb2ErFGCOqt0KQfXuyKWLhpnNHCdRzZdxi018Q@mail.gmail.com/

 [1]
Suggested-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20250112152946.761150-4-ojeda@kernel.org