doc: Document suitability of IBM Verse for kernel development

IBM Verse is a web UI around Lotus Domino mail servers (much like
the Lotus Notes client talks to Domino servers).

For various reasons, it is not at all suitable for kernel development,
all of which have been raised (repeatedly) internally.

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
Acked-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>