Merge branch 'sb/doc-config-submodule-update'

* sb/doc-config-submodule-update:
  Documentation/config: clarify the meaning of submodule.<name>.update

Documentation/config.txt

@@ -3085,10 +3085,14 @@ submodule.<name>.url::
 	See linkgit:git-submodule[1] and linkgit:gitmodules[5] for details.
 
 submodule.<name>.update::
-	The default update procedure for a submodule. This variable
-	is populated by `git submodule init` from the
-	linkgit:gitmodules[5] file. See description of 'update'
-	command in linkgit:git-submodule[1].
+	The method by which a submodule is updated by 'git submodule update',
+	which is the only affected command, others such as
+	'git checkout --recurse-submodules' are unaffected. It exists for
+	historical reasons, when 'git submodule' was the only command to
+	interact with submodules; settings like `submodule.active`
+	and `pull.rebase` are more specific. It is populated by
+	`git submodule init` from the linkgit:gitmodules[5] file.
+	See description of 'update' command in linkgit:git-submodule[1].
 
 submodule.<name>.branch::
 	The remote branch name for a submodule, used by `git submodule