migration guide update for network changes

Author: henry416

documentation/release-notes/migration-guide.4.0.0.md

@@ -7,6 +7,7 @@ This document serves as both a breaking change notification and migration guide
 - [Breaking changes to Compute cmdlets](#breaking-changes-to-compute-cmdlets)
 - [Breaking changes to EventHub cmdlets](#breaking-changes-to-eventhub-cmdlets)
 - [Breaking changes to Insights cmdlets](#breaking-changes-to-insights-cmdlets)
+- [Breaking changes to Network cmdlets](#breaking-changes-to-network-cmdlets)
 - [Breaking changes to ServiceBus cmdlets](#breaking-changes-to-servicebus-cmdlets)
 - [Breaking changes to Sql cmdlets](#breaking-changes-to-sql-cmdlets)
 - [Breaking changes to Storage cmdlets](#breaking-changes-to-storage-cmdlets)
@@ -171,6 +172,13 @@ Set-AzureRmDiagnosticSettings
 Update-AzureRmDiagnosticSettings
 ```
 
+## Breaking changes to Network cmdlets
+
+The following cmdlets were affected this release:
+
+### New-AzureRmVirtualNetworkGatewayConnection
+- `EnableBgp` parameter has been changed to take a `boolean` instead of a `string`
+
 ## Breaking changes to ServiceBus cmdlets
 
 The following cmdlets were affected this release: