Comparing Shakespeare's Macbeth to the historical Macbeth.What would be a good intro paragraph talking about how Shakespeare altered the dramatic...

Your opening paragraph should probably note how
Shakespeare was not attempting an historical play in Macbeth. 
While Holinshead's Chronicles form the basis for much of his information, Shalespeare
took that information and changed and shaped it to help make a dramatic story.  In that
way, it is much like Arthur Miller's The Crucible, which takes some
historical information about the Salem Witch Trials and then adds details and even
changes some characters to make the drama effective.  (Walt Disney Studios did much the
same thing with some of their most famous cartoon adaptations such as Beauty
and the Beast or The Little
Mermaid.)

Shakespeare was also keenly aware of
his audience.  King James I of Engliand (who was also James VI of Scotland) was
interested in witches.  James I was also a descendent of Banquo's.  Both of these ideas
are brought into the plays as well.