Add output for code snippets

In pages like this it would be useful to have the output of the code snippets. For example, it's not obvious that the output of:

adapter.GetPhysicalAddress().ToString();

Will be in the format `AABBCCDDEEFF`. Being a MAC address I would have expected the display representation to be `AA:BB:CC:DD:EE:FF`.

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#### Document Details

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* ID: 87d7394a-3f17-943a-fa63-7d0ee3df49c4
* Version Independent ID: 93f4c822-8a80-2147-41c5-a69ca5b722f8
* Content: [NetworkInterface Class (System.Net.NetworkInformation)](https://docs.microsoft.com/en-us/dotnet/api/system.net.networkinformation.networkinterface?view=netframework-4.7.1)
* Content Source: [xml/System.Net.NetworkInformation/NetworkInterface.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.Net.NetworkInformation/NetworkInterface.xml)
* Product: **.net**
* GitHub Login: @dotnet-bot
* Microsoft Alias: **bobdel**