Adding minimum required netlab release to README files

Author: ipspace

VRF/vrf-lite-hosts/README.md

@@ -36,6 +36,8 @@ The `multi-vrf.yml` topology contains two isolated VRFs:
 
 After starting the lab, h1 should be able to ping h2 but not h3 or h4, and h3 should be able to ping h4 but not h1 or h2.
 
+**Note:** the lab topology uses the [_VRF links_](https://netsim-tools.readthedocs.io/en/latest/module/vrf.html#module-vrf-links) functionality introduced in [netlab release 1.5.1](https://netsim-tools.readthedocs.io/en/latest/release/1.5.html#release-1-5-1).
+
 ## Inter-VRF Route Leaking
 
 The `vrf-route-leaking.yml` topology contains three VRFs:

VXLAN/vxlan-bridging/README.md

@@ -6,6 +6,8 @@ This directory contains *netlab* topology file for a simple VXLAN bridging scena
 
 After starting the lab, h1 should be able to ping h2, and h3 should be able to ping h4, but there should be no traffic routed between the VLANs. Also, the VLAN hosts should not be able to access the switches.
 
+**Note:** the lab topology uses the _[VLAN links](https://netsim-tools.readthedocs.io/en/latest/module/vlan.html#module-vlan-creating-access-links)_ functionality introduced in [netlab release 1.5.1](https://netsim-tools.readthedocs.io/en/latest/release/1.5.html#release-1-5-1).
+
 ## Changing Device Types
 
 This topology can be used with all network devices supporting VLAN, VXLAN, and OSPF configuration modules, and all virtualization providers supported by *netlab*: