Add learning material for LoRaWAN relay basics

[pradeeka7]

Summary

Add learning material for LoRaWAN relay basics.

Why do we need this ?

Still we don't have any learning materials for relays.

What is already there? What do you see now?

...

What is missing? What do you want to see?

...

How do you propose to document this?

• LoRaWAN network architecture with relay
• Relay features
• WOR and WOR-ACK frames and message flow diagrams
• Device identifiers and root keys used in relays
• Uplink message format
• A few use cases

Can you do this yourself and submit a Pull Request?

Yes

[pradeeka7]

@nejraselimovic pls. assign this issue to me.