Adding a new example for Netmiko and Loopback Manipulation

[hpreston]

This is a CLI example using Netmiko and the DevNet Sandbox.

[hpreston]

Hey... I'd love to merge this in. Can you please do the following.

1. Add a requirements.txt file for all python requirements
2. Add a readme to the example folder describing what it does.
3. Update the main repo README to add the example to the table.

[hpreston]

Changes have been made!