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/ [2] Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name> Signed-off-by: Junio C Hamano <gitster@pobox.com>