Here I will embed PlantUML markup to generate a sequence diagram.
I can include as many plantuml segments as I want in my Markdown, and the diagrams can be of any type supported by PlantUML.
@startuml
skinparam backgroundColor #EEEBDC
skinparam handwritten true
actor Customer
Customer -> "login()" : username & password
"login()" -> Customer : session token
activate "login()"
Customer -> "placeOrder()" : session token, order info
"placeOrder()" -> Customer : ok
Customer -> "logout()"
"logout()" -> Customer : ok
deactivate "login()"
@enduml