Documentation of callIds

[rluvaton]

Would you be open for PR to document the callIds property?

The reason it's needed is because let's say I have 2 function fn1 and fn2

And want to test assert the following

fn1();
fn2();
fn1();
fn2();

Currently I can't do that with the current assertions but I want to open it so I can add support for other assertions library to use (my sinon-jest-marchers specifically)