Add note about dns-prefetch as fallback (vercel#30385)

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `yarn lint`


Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>

errors/google-font-preconnect.md

@@ -12,6 +12,9 @@ Add `rel="preconnect"` to the Google Font domain `<link>` tag:
 <link rel="preconnect" href="https://fonts.gstatic.com" />
 ```
 
+Note: a **separate** link with `dns-prefetch` can be used as a fallback for browsers that don't support `preconnect` although this is not required.
+
 ### Useful Links
 
 - [Preconnect to required origins](https://web.dev/uses-rel-preconnect/)
+- [Preconnect and dns-prefetch](https://web.dev/preconnect-and-dns-prefetch/#resolve-domain-name-early-with-reldns-prefetch)