SubmittingPatches: discourage common Linux trailers

SubmittingPatches: discourage common Linux trailers

The Linux Kernel regularly uses trailers (or “tags”) `Fixes` and
`Link`. Sometimes people submit patches to this project with them.
They have their use in that project but it is not clear what purpose
they would serve here.

For `Fixes`: Linux has many trees, and applying patches with
cherry-picks is common. A `Fixes` trailer in commit C2 pointing to
commit C1 helps the cherry-picker figure out that she probably needs
C2 if she wants to apply C1. See linux/d5d6281a (checkpatch: check for
missing Fixes tags, 2024-06-11):[1]

    Why are stable patches encouraged to have a fixes tag?  Some people
    mark their stable patches as "# 5.10" etc.  This is useful but a
    Fixes tag is still a good idea.  For example, the Fixes tag helps in
    review.  It helps people to not cherry-pick buggy patches without
    also cherry-picking the fix.

In contrast the Git project has few trees (to my knowledge), and there
is much less need to cherry-pick fixes as opposed to either using
backmerges or rebasing all of the downstream tree’s commits on top of
git.git `master` from time to time.

This project does regularly mention what commits a patch/commit fixes,
but that is done inline in the commit message proper (cf. the trailer
block of the message).

For `Link`: These are used both to link back to the patch submission as
well as with footnotes. In contrast this project has `refs/notes/amlog`
for linking back to the patch submissions, and footnotes are only used
in the commit message proper.

† 1: Commit linux/d5d6281a has “linux” in front of it since this commit
     is from the Linux Kernel, not Git. Example of a Linux tree—as well
     as an example of `Link`—is [2].

Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>