docs: filesystems: convert isofs.txt to ReST

- Add a SPDX header;
- Add a document title;
- Some whitespace fixes and new line breaks;
- Add table markups;
- Add lists markups;
- Add it to filesystems/index.rst.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/ec16dc09d0c23bb0c1af3d3f33a96896083a1d36.1581955849.git.mchehab+huawei@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/filesystems/index.rst

@@ -71,6 +71,7 @@ Documentation for filesystem implementations.
    hfsplus
    hpfs
    inotify
+   isofs
    fuse
    overlayfs
    virtiofs

Documentation/filesystems/isofs.txt → Documentation/filesystems/isofs.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+==================
+ISO9660 Filesystem
+==================
+
 Mount options that are the same as for msdos and vfat partitions.
 
+  =========	========================================================
   gid=nnn	All files in the partition will be in group nnn.
   uid=nnn	All files in the partition will be owned by user id nnn.
   umask=nnn	The permission mask (see umask(1)) for the partition.
+  =========	========================================================
 
 Mount options that are the same as vfat partitions. These are only useful
 when using discs encoded using Microsoft's Joliet extensions.
+
+ ==============	=============================================================
  iocharset=name Character set to use for converting from Unicode to
 		ASCII.  Joliet filenames are stored in Unicode format, but
 		Unix for the most part doesn't know how to deal with Unicode.
 		There is also an option of doing UTF-8 translations with the
 		utf8 option.
   utf8          Encode Unicode names in UTF-8 format. Default is no.
+ ==============	=============================================================
 
 Mount options unique to the isofs filesystem.
+
+ ================= ============================================================
   block=512        Set the block size for the disk to 512 bytes
   block=1024       Set the block size for the disk to 1024 bytes
   block=2048       Set the block size for the disk to 2048 bytes
@@ -39,10 +52,13 @@ Mount options unique to the isofs filesystem.
 		   recreate previous unhide behavior
   session=x        Select number of session on multisession CD
   sbsector=xxx     Session begins from sector xxx
+ ================= ============================================================
 
 Recommended documents about ISO 9660 standard are located at:
-http://www.y-adagio.com/
-ftp://ftp.ecma.ch/ecma-st/Ecma-119.pdf
+
+- http://www.y-adagio.com/
+- ftp://ftp.ecma.ch/ecma-st/Ecma-119.pdf
+
 Quoting from the PDF "This 2nd Edition of Standard ECMA-119 is technically
 identical with ISO 9660.", so it is a valid and gratis substitute of the
 official ISO specification.