Functions for displaying PNG files are missing from PicoGraphics readmes

[helgibbons]

They can mostly be deduced from the JPG functions, but they would be less of a mystery if we added them to the relevant readmes :)

[barchard]

I can't seem to get import pngdec to work like import jpegdec does. What did you use for your import statement? Thanks

[helgibbons]

@barchard This works for me on a Tufty 2040. I think pngdec was quite a recent addition, so it might be worth downloading the most MicroPython image for your board if you're having trouble?

import picographics
import pngdec

display = picographics.PicoGraphics(display=picographics.DISPLAY_TUFTY_2040)

# Create a new PNG decoder for our PicoGraphics
p = pngdec.PNG(display)

# Open the PNG file
p.open_file("filename.png")

# Decode the PNG
p.decode(0, 0)

# Display the result
display.update()

[thirdr]

The README here has been updated now :).