E.T. looks at you and smiles. His croaking voice is somehow comforting.
"Alan, the line lies..."
He touches his finger to your heart.
"...In here."
There are no rules for this - it's entirely down to you. Have a look at Wikipedia for the docs you watched and see what liberties they took and what you feel comfortable with.
(One of the most egregious examples is Searching for Sugar Man - a superb documentary about a forgotten musician... Which annoyingly has a premise based almost entirely on lies and withholding information.)
I would personally keep things as real as possible but that is entirely my personal view - I certainly wouldn't hold it against anyone to sex things up a bit. The important thing is to keep the journey on track.
For the specific example you gave the truth is enough I think - it's an amusing image that has some drama in its own right!