Add information on subnetworks.

1/PAR/notes/pt-docs.md

@@ -15,6 +15,13 @@ enable secret <password>
 username <usuario> privilege 1 password 0 <password>
 ```
 
+## Sub-Interfaces
+
+```
+int <if>.<sub-if> # e.g. fa0/1.1
+encapsulation dot1Q <net> [native]
+```
+
 ## Enrutamiento
 
 ### Dinámico