Documentation: fuse: Consolidate FUSE docs into its own subdirectory

All four FUSE docs are currently in upper-level
Documentation/filesystems/ directory, but these are distinct as a group
of its own. Move them into Documentation/filesystems/fuse/ subdirectory.

Signed-off-by: Bagas Sanjaya <[e-mail]>
Acked-by: Jeff Layton <[e-mail]>
Signed-off-by: Miklos Szeredi <[e-mail]>

Documentation/filesystems/fuse-io.rst Documentation/filesystems/fuse/fuse-io.rst

···
 .. SPDX-License-Identifier: GPL-2.0
 
 ==============
-Fuse I/O Modes
+FUSE I/O Modes
 ==============
 
 Fuse supports the following I/O modes:

Documentation/filesystems/fuse.rst Documentation/filesystems/fuse/fuse.rst

···
 .. SPDX-License-Identifier: GPL-2.0
 
-====
-FUSE
-====
+=============
+FUSE Overview
+=============
 
 Definitions
 ===========

Documentation/filesystems/fuse/index.rst

···
+.. SPDX-License-Identifier: GPL-2.0
+
+======================================================
+FUSE (Filesystem in Userspace) Technical Documentation
+======================================================
+
+.. toctree::
+   :maxdepth: 2
+   :numbered:
+
+   fuse
+   fuse-io
+   fuse-io-uring
+   fuse-passthrough

Documentation/filesystems/index.rst

···
    hfs
    hfsplus
    hpfs
-   fuse
-   fuse-io
-   fuse-io-uring
-   fuse-passthrough
+   fuse/index
    inotify
    isofs
    nilfs2

MAINTAINERS

···
 S:	Maintained
 W:	https://github.com/libfuse/
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git
-F:	Documentation/filesystems/fuse*
+F:	Documentation/filesystems/fuse/*
 F:	fs/fuse/
 F:	include/uapi/linux/fuse.h
 F:	tools/testing/selftests/filesystems/fuse/