the intro is a shuffle of the G chord (320033) strummed once down, then shuffle ur hand 
across the strings in an up down motion and then the chord played again, like a fill 
chords, repeat this until the rest of the chords start, thats the strumming pattern.

EI--3--------------2---------------3-----------------|
BI--3------------1-3-----------1---3-----------------|
GI--0------------0-2-----------0---0-----------------|
DI--0----------2-2-------------2-2-0-----------------|
AI--2----------2-3-------------3-2-2-----------------|
EI--3------------------------------3-----------------|

and the pretty much repeats that the whole way through