GitHub recently added mermaid rendering to their markdown dialect, making it simple to render your diagrams, whether in a readme or just thrown together in a gist.
As soon as you create a new gist (remembering to use the .md extension, to enable preview), you can easily draw a sequence diagram:
```mermaid
sequenceDiagram
Alice->>John: Hello John, how are you?
John-->>Alice: Great!
Alice-)John: See you later!
```

or finite automata:
```mermaid
stateDiagram-v2
state fork_state <<fork>>
[*] --> fork_state
fork_state --> State2
fork_state --> State3
state join_state <<join>>
State2 --> join_state
State3 --> join_state
join_state --> State4
State4 --> [*]
```
