BreakingChanges: document that we do not plan to deprecate git-checkout

The git-checkout(1) command is seen by many as hard to understand
because it connects two somewhat unrelated features: switching between
branches and restoring worktree files from arbitrary revisions. In 2019,
we thus implemented two new commands git-switch(1) and git-restore(1) to
split out these separate concerns into standalone functions.

This "replacement" of git-checkout(1) has repeatedly triggered concerns
for our userbase that git-checkout(1) will eventually go away. This is
not the case though: the use of that command is still widespread, and it
is not expected that this will change anytime soon.

Document that all three commands will remain for the foreseeable future.
This decision may be revisited in case we ever figure out that most
everyone has given up on any of the commands.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

Documentation/BreakingChanges.txt

@@ -121,3 +121,15 @@ Some features have gained newer replacements that aim to improve the design in
 certain ways. The fact that there is a replacement does not automatically mean
 that the old way of doing things will eventually be removed. This section tracks
 those features with newer alternatives.
+
+* The features git-checkout(1) offers are covered by the pair of commands
+  git-restore(1) and git-switch(1). Because the use of git-checkout(1) is still
+  widespread, and it is not expected that this will change anytime soon, all
+  three commands will stay.
++
+This decision may get revisited in case we ever figure out that there are
+almost no users of any of the commands anymore.
++
+Cf. <[email protected]>,
+<[email protected]>,
+<[email protected]>.