Switch to using license like MIT, GPL, etc.

Currently it looks like this code is not available for direct reuse. The repo is marked private in the package.json
```
"private": true,
```
https://github.com/scanapp-org/html5-qrcode-react/blob/main/package.json#L4

and I did not spot a license file or similar.

If this is the intended state or not thank you for making you code available for reading and educational purposes.