Documentation: always respect core.worktree if set

The value of core.worktree in a ".git/config" is honored even when it
differs from the directory that has the ".git" directory as its
subdirectory.  This is likely to be a misconfiguration, so warn users
about it.  Also, drop the part of the documentation that incorrectly
claimed that we ignore such a misconfigured value.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -297,17 +297,24 @@ false), while all other repositories are assumed to be bare (bare
 = true).
 
 core.worktree::
-	Set the path to the working tree.  The value will not be
-	used in combination with repositories found automatically in
-	a .git directory (i.e. $GIT_DIR is not set).
+	Set the path to the root of the work tree.
 	This can be overridden by the GIT_WORK_TREE environment
 	variable and the '--work-tree' command line option. It can be
-	a absolute path or relative path to the directory specified by
-	--git-dir or GIT_DIR.
-	Note: If --git-dir or GIT_DIR are specified but none of
+	an absolute path or a relative path to the .git directory,
+	either specified by --git-dir or GIT_DIR, or automatically
+	discovered.
+	If --git-dir or GIT_DIR are specified but none of
 	--work-tree, GIT_WORK_TREE and core.worktree is specified,
-	the current working directory is regarded as the top directory
-	of your working tree.
+	the current working directory is regarded as the root of the
+	work tree.
++
+Note that this variable is honored even when set in a configuration
+file in a ".git" subdirectory of a directory, and its value differs
+from the latter directory (e.g. "/path/to/.git/config" has
+core.worktree set to "/different/path"), which is most likely a
+misconfiguration.  Running git commands in "/path/to" directory will
+still use "/different/path" as the root of the work tree and can cause
+great confusion to the users.
 
 core.logAllRefUpdates::
 	Enable the reflog. Updates to a ref <ref> is logged to the file