api.md: document using '-' value as default tailnet
@@ -355,6 +355,13 @@ GET /api/v2/tailnet/alice@gmail.com/...
curl https://api.tailscale.com/api/v2/tailnet/alice@gmail.com/...
```
+Alternatively, you can specify the value "-" to refer to the default tailnet of
+the authenticated user making the API call. For example:
+```
+GET /api/v2/tailnet/-/...
+curl https://api.tailscale.com/api/v2/tailnet/-/...
+```
+
Tailnets are a top-level resource. ACL is an example of a resource that is tied to a top-level tailnet.
For more information on Tailscale networks/tailnets, click [here](https://tailscale.com/kb/1064/invite-team-members).
