udf: Update mount option documentation

	iocharset=	Set the NLS character set

The uid= and gid= options need a bit more explaining.  They will accept a

decimal numeric value which will be used as the default ID for that mount.

They will also accept the string "ignore" and "forget".  For files on the disk

that are owned by nobody ( -1 ), they will instead look as if they are owned

by the default ID.  The ignore option causes the default ID to override all

IDs on the disk, not just -1.  The forget option causes all IDs to be written

to disk as -1, so when the media is later remounted, they will appear to be

owned by whatever default ID it is mounted with at that time.

decimal numeric value and all inodes on that mount will then appear as

belonging to that uid and gid.  Mount options also accept the string "forget".

The forget option causes all IDs to be written to disk as -1 which is a way

of UDF standard to indicate that IDs are not supported for these files .

For typical desktop use of removable media, you should set the ID to that

of the interactively logged on user, and also specify both the forget and

ignore options.  This way the interactive user will always see the files

on the disk as belonging to him.

For typical desktop use of removable media, you should set the ID to that of

the interactively logged on user, and also specify the forget option.  This way

the interactive user will always see the files on the disk as belonging to him.

The remaining are for debugging and disaster recovery: