docs: bug-bisect: add a note about bisecting -next

Explicitly mention how to bisect -next, as nothing in the kernel tree
currently explains that bisects between -next versions won't work well
and it's better to bisect between mainline and -next.

Co-developed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/ec19d5fc503ff7db3d4c4ff9e97fff24cc78f72a.1730808651.git.linux@leemhuis.info

Author: knurd

Documentation/admin-guide/bug-bisect.rst

@@ -108,6 +108,27 @@ a fully reliable and straight-forward way to reproduce the regression, too.*
 With that the process is complete. Now report the regression as described by
 Documentation/admin-guide/reporting-issues.rst.
 
+Bisecting linux-next
+--------------------
+
+If you face a problem only happening in linux-next, bisect between the
+linux-next branches 'stable' and 'master'. The following commands will start
+the process for a linux-next tree you added as a remote called 'next'::
+
+  git bisect start
+  git bisect good next/stable
+  git bisect bad next/master
+
+The 'stable' branch refers to the state of linux-mainline that the current
+linux-next release (found in the 'master' branch) is based on -- the former
+thus should be free of any problems that show up in -next, but not in Linus'
+tree.
+
+This will bisect across a wide range of changes, some of which you might have
+used in earlier linux-next releases without problems. Sadly there is no simple
+way to avoid checking them: bisecting from one linux-next release to a later
+one (say between 'next-20241020' and 'next-20241021') is impossible, as they
+share no common history.
 
 Additional reading material
 ---------------------------