Update temporal-nexus.mdx

Author: stephanos

docs/production-deployment/self-hosted-guide/temporal-nexus.mdx

@@ -125,7 +125,7 @@ target an external URL (`--target-url`), which is experimental and not covered h
    requests forward to the active Cluster when a client connects to a standby: use
    `all-apis-forwarding` for all client APIs, or `selected-apis-forwarding` for a
    fixed subset that includes `StartNexusOperationExecution` (used to start a
-   standalone Nexus Operation).
+   [standalone Nexus Operation](/standalone-nexus-operation)).
 
 ### What to expect on failover