README does not provide enough info for new users

[dbenader]

Hello there!

I would love to integrate this library into my app, but I am finding it hard to learn how to use. Perhaps I am missing something, but I feel the current README provides very little information about creating graphs. For example, we see the following code block in the 'usage' section:

`function App() {
const priceHistory = usePriceHistory('ethereum')

return
}`

However, there is no information on what the format should be for the data passed to the points property of LineGraph, or what the 'usePriceHistory' function actually does/returns.

[Montchy]

Thank you for reporting this issue, but it is a duplicate of:

-#51