fixed wrong doc link (#1449)

* fixed wrong doc link

* directly referenced file

Co-authored-by: Jack Gerrits <jackgerrits@users.noreply.github.com>

* Update website/docs/Use-Cases/agent_chat.md

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Co-authored-by: Jack Gerrits <jackgerrits@users.noreply.github.com>
Co-authored-by: Chi Wang <wang.chi@microsoft.com>