How to draw diagrams using markdown?

Simple Sequence Diagram

sequenceDiagram
Alice->Bob: Hello Bob, how are you?
Note right of Bob: Bob thinks
Bob-->Alice: I am good thanks!

flow
st=>start: Start
op=>operation: Your Operation
cond=>condition: Yes or No?
e=>end

st->op->cond
cond(yes)->e
cond(no)->op

Complex Sequence Diagram

  sequenceDiagram
    Alice->>Bob: Hello Bob, how are you?
    alt is sick
    Bob->>Alice: Not so good :(
    else is well
    Bob->>Alice: Feeling fresh like a daisy
    end
    opt Extra response
    Bob->>Alice: Thanks for asking
    end