Prettify React code

[40thieves]

Try setting up Prettier for the React branch, with Github Actions CI. Config stolen from here.

Not an expert with Actions, so I guess we'll see if this works.

[40thieves]

Not an expert with Actions, so I guess we'll see if this works.

I guess not... maybe it has to be merged to main before it works?

[40thieves]

maybe it has to be merged to main before it works?

Hmm just realised that this isn't targeting main... and it's nested inside client. So maybe I'll just drop the Actions bit for now. I think we can probably just assume that folks have prettier set up in their editors.

[40thieves]

Thanks!