Add intruction to close PPPoE connection in SiAB with SD-BNG

Change-Id: Ied0e80de3b154e0955f7a6cdf62d8daabc4a9388
diff --git a/profiles/seba/siab.md b/profiles/seba/siab.md
index c551182..ee99501 100644
--- a/profiles/seba/siab.md
+++ b/profiles/seba/siab.md
@@ -774,7 +774,15 @@
 and reaches the upstream router as standard IP traffic.
 The PPPoE tunnel termination is performed entirely in the data plane by the ASG switch.
 
-That’s it. Currently it’s not possible to send traffic to destinations on the Internet.
+Currently it’s not possible to send traffic to destinations on the Internet.
+
+### PPPoE RG close PPPoE connection
+
+Finally, run:
+```bash
+poff seba
+```
+This command will close the PPPoE connection sending a termination request to the PPPoE server.
 
 ## Restarting SEBA-in-a-Box after a reboot