Update dead links in React CIAM tutorial

https://github.com/Azure-Samples/ms-identity-ciam-javascript-tutorial/blob/main/1-Authentication/1-sign-in-react/README.md#create-user-flows (which [links this dead tutorial](https://github.com/microsoft/entra-previews/blob/PP2/docs/3-Create-sign-up-and-sign-in-user-flow.md))

Sort of pivotal links to this tutorial's usefulness could be updated

### This issue is for a: (mark with an `x`)
```
- [ ] bug report -> please search issues before submitting
- [ ] feature request
- [x] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)
```

Open the 1-Authentication/1-sign-in-react/README.md file and inspect the #create-user-flows link, then find the current destination replacing the dead entra-previews tutorial. The work is done when the pivotal link resolves to the appropriate current user-flow documentation and the README no longer points to the dead page.

Written by the indexing model from the issue text.