Update README documentation for `<SecureRoute>` incompatibility with React Router v6

[gavinr-maps]

Describe the bug

It was discussed here that <SecureRoute> cannot be used with React Router v6. This fact was confirmed by @jaredperreault-okta here, and Jared linked to this sample which does not use the <SecureRoute> component.

Based on the above, <SecureRoute> is not compatible with React Router v6. Given that React Router v6 has been out for almost 2 years, I think the documentation in this project's README should assume that users are using React Router v6 (and thus cannot use <SecureRoute> 😟). That involves:

1. Updating this sample:
   
2. Updating the wording here
   

Reproduction Steps?

See the README links above.

SDK Versions

n/a

Additional Information

No response

[Lcharvol]

Someone is working on this bug? react-router v6 is up since 2 years now...

[guushamann]

2,5 years now...