Add documentation to clarify algorithms for Mark Joins

[jonathanc-n]

Is your feature request related to a problem or challenge?

that would be nice to show as an example, it is challenging to read algorithms for upcoming contributors, but it can be done as follow up PR

Quoted from @comphead in #16083. Adding docs for mark joins to make it easier for people reading the code to have an easier time understanding 😄

Describe the solution you'd like

No response

Describe alternatives you've considered

No response

Additional context

No response

[jonathanc-n]

take