The examples are generated by GitVersion tests, there are a number of services which will then turn the sequence diagram text into an image to use in the docs. Here are some links which could be useful
The tests are quite simple. Using the methods on the fixture itself will
record that action in the sequence diagram. If you do not want the action
recorded perform the action directly on the repository (fixture.Repository.)
The tests for the examples should all live at DocumentationSamples.cs