Added some PicoGraphics based MP examples for the PicoUnicorn

[ahnlak]

As mentioned on the forum, the examples for the Pico Unicorn Pack used the 'native' graphics, rather than the newer PicoGraphics based ones.

Duplicated the two existing examples into -picographics versions, and added a version of fire-effect.py from the other Unicorns' examples, turned on it's side to get a bit more height displayed!

Also updated the PicoGraphics readme to (a) acknowledge the existence of the Pico Unicorn, and (b) mention that the special update() handling applies to all Unicorns, not just the Galactic.

[helgibbons]

Thanks very much for this :)

All looks good, though the fire example doesn't seem to be using any of the LEDs in the right-most column of the display - was this intentional?

[ahnlak]

I'd love to say it was, but no - it was more the side effect of trying to work out how to turn the fire effect on it's side without breaking anything :-)

(looking at it, I seem to have removed a +1 that I didn't fully comprehend, and failed to notice this was the result - I can push a fix if that doesn't make the PR too untidy?)

[helgibbons]

That would be super, thanks!