New link needed about Entry guards in Managing Identities

In https://tb-manual.torproject.org/managing-identities/ we say:

For more information about Guards, consult the [FAQ](https://www.torproject.org/docs/faq#EntryGuards) and Support Portal.

But https://www.torproject.org/docs/faq#EntryGuards leads me to support.torproject.org homepage.

We should replace that link, maybe we already have the Entry Guard FAQ somewhere in support.tpo.