MQTT rationale + figure

- https://aws.amazon.com/what-is/mqtt/ (decoupling)

```mermaid
flowchart LR
    id1((Synchronization)) <--> id2
    id2((Space)) <--> id3
    id3((Time)) <--> id1
```

-----

```mermaid
sequenceDiagram
    Publisher->>Subscriber: Example data flow.
```

Related: #19 