update supported standards

Author: robswain

articles/private-5g-core/statement-of-compliance.md

@@ -32,6 +32,7 @@ All packet core network functions are compliant with Release 15 of the 3GPP spec
 - TS 29.274: 3GPP Evolved Packet System (EPS); Evolved General Packet Radio Service (GPRS) Tunneling Protocol for Control plane (GTPv2-C); Stage 3.
 - TS 33.401: 3GPP System Architecture Evolution (SAE); Security architecture.
 - TS 36.413: Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP).
+- TS 29.061: Interworking between the Public Land Mobile Network (PLMN) supporting packet based services and Packet Data Networks (PDN)
 
 ### 5G handover procedures