link to theme-patternfly-org in the react docs readme is broken

The repo doesn't have a `master` branch but a `main` branch instead
https://github.com/patternfly/patternfly-react/blob/7ef55a0e7fc984b853657c3b86e14e4e0f6ffe1c/packages/react-docs/README.md?plain=1#L3
```
This project uses [theme-patternfly-org](https://github.com/patternfly/patternfly-org/tree/master/packages/theme-patternfly-org) to render example MD files.
```