Reword documentation regarding tid-time function.

tid-time is a function, not a macro. This is a pretty trivial, but I thought I'd fork the repository so I could update this code if need be, and also maybe look at the other parts of TW5.

Incidentally, I called the tid-time function when editing this. You might want a different time, not sure. (I'm in India.) 

Finally, I have a local commit signing the Contributer's license, if that's a necessary prerequisite for docs changes.