Task: add concrete use cases to the readme

[nicolo-ribaudo]

There are multiple use cases in https://github.com/tc39/proposal-decimal/issues/3, which should be added to the readme or a separate docs page.

The temporal cookbook has been helpful for this, showing concrete use cases and concrete solutions.

[ptomato]

I did some work on this in a previous iteration of the proposal and came up with these cookbook recipes. They'll certainly need to be adjusted to work with the proposal as it is now.

• https://github.com/Igalia/decimal-playground/blob/main/src/examples/scientific.js - printing physics constants in scientific notation
• https://github.com/Igalia/decimal-playground/pull/1 - React calculator app
• https://gist.github.com/ptomato/6acf6b2eb8fe0a52ead93baeeedb02f6 - naive Bayes classifier

[hipstersmoothie]

I found when building my window splitter I needed really precise math to get the right result

https://react-window-splitter-six.vercel.app/

For this I turned to big.js

[jessealama]

I've finally managed to get around to making a little cookbook, something we've wanted for a long time. It's not as cool as Temporal's but I think it's a good start.