Add images from coloured-spreadsheet example to documentation

[Dan Brickley]

Readme has dud link to the multicoloured spreadsheet - https://github.com/Swirrl/table2qb/blob/master/examples/regional-trade/all-colour-coded.ods I think

i can’t see .ods files on my phone but wondered if it is worth extracting a static image?

[Robin Gower]

Ah yeah that was a relative link copied from the other readme. I've corrected that now.

Pictures are a great idea. Perhaps with a star-layout to show the relationships.

Let's keep this issue open for that.