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 <[e-mail]>
Link: https://lore.kernel.org/r/ec16dc[e-mail]
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/filesystems/index.rst

···
    hfsplus
    hpfs
    inotify
+   isofs
    fuse
    overlayfs
    virtiofs

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
+  check=relaxed    Matches filenames with different cases
+  check=strict     Matches only filenames with the exact same case
+  cruft            Try to handle badly formatted CDs.
+  map=off          Do not map non-Rock Ridge filenames to lower case
+  map=normal       Map non-Rock Ridge filenames to lower case
+  map=acorn        As map=normal but also apply Acorn extensions if present
+  mode=xxx         Sets the permissions on files to xxx unless Rock Ridge
+		   extensions set the permissions otherwise
+  dmode=xxx        Sets the permissions on directories to xxx unless Rock Ridge
+		   extensions set the permissions otherwise
+  overriderockperm Set permissions on files and directories according to
+		   'mode' and 'dmode' even though Rock Ridge extensions are
+		   present.
+  nojoliet         Ignore Joliet extensions if they are present.
+  norock           Ignore Rock Ridge extensions if they are present.
+  hide		   Completely strip hidden files from the file system.
+  showassoc	   Show files marked with the 'associated' bit
+  unhide	   Deprecated; showing hidden files is now default;
+		   If given, it is a synonym for 'showassoc' which will
+		   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
+
+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.

Documentation/filesystems/isofs.txt

···
-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
-  check=relaxed Matches filenames with different cases
-  check=strict  Matches only filenames with the exact same case
-  cruft         Try to handle badly formatted CDs.
-  map=off       Do not map non-Rock Ridge filenames to lower case
-  map=normal    Map non-Rock Ridge filenames to lower case
-  map=acorn     As map=normal but also apply Acorn extensions if present
-  mode=xxx      Sets the permissions on files to xxx unless Rock Ridge
-		extensions set the permissions otherwise
-  dmode=xxx     Sets the permissions on directories to xxx unless Rock Ridge
-		extensions set the permissions otherwise
-  overriderockperm Set permissions on files and directories according to
-		'mode' and 'dmode' even though Rock Ridge extensions are
-		present.
-  nojoliet      Ignore Joliet extensions if they are present.
-  norock        Ignore Rock Ridge extensions if they are present.
-  hide		Completely strip hidden files from the file system.
-  showassoc	Show files marked with the 'associated' bit
-  unhide	Deprecated; showing hidden files is now default;
-		If given, it is a synonym for 'showassoc' which will
-		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
-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.