[PATCH mtd-www] doc/ubi.xml: clarify from the start that block device on UBI is read-only

[Richard Weinberger]

----- Ursprüngliche Mail -----
> Von: "Thomas Petazzoni" <thomas.petazzoni at bootlin.com>
> In the introduction, the sentence that introduces ubiblock might let
> one think that any read/write block filesystem can be used on top of
> UBI, which is wrong. So clarify from the start that this is read-only.
> 
> Signed-off-by: Thomas Petazzoni <thomas.petazzoni at bootlin.com>

The first drafts of ubiblock have been read/write, maybe that's a left over.

Acked-by: Richard Weinberger <richard at nod.at>

Thanks,
//richard