llava : add explicit instructions for llava-1.6 (#5611)

This commit contains a suggestion for the README.md in the llava
example. The suggestion adds explicit instructions for how to convert
a llava-1.6 model and run it using llava-cli.

The motivation for this is that having explicit instructions similar to
the 1.5 instructions will make it easier for users to try this out.

Signed-off-by: Daniel Bevenius <daniel.bevenius@gmail.com>