Awesome song many people have wrote different riffs, this is the way i learnt it and believe it goes. 

INTRO

E|------------------------------------------------------------|
B|------------------------------------------------------------|
G|----------------------8-6-----------------------------------|
D|------6-8b(10)--6---6-----6-------6-3b(5)--------5-3-5------|
A|--8-8-------------6----------4-4-------------4-3------------|
E|------------------------------------------------------------|
  


VERSE
E|---------------------------------------------------------------|
B|---------------------------------------------------------------|
G|---------------------------------------------------------------|
D|--x-x-10---x-x-10---x-x-10---x-x-10---x-x-8--x-x-8--x-x-8------|
A|--x-x-10---x-x-10---x-x-10---x-x-10---x-x-8--x-x-8--x-x-8------|
E|--x-x--8---x-x--8---x-x--8---x-x--8---x-x-6--x-x-6--x-x-6------|
 Pm . .      . .      . .      . .      . .    . .    . . 

VERSE cont....
E|--------------------------------------------------------------|
B|--------------------------------------------------------------|
G|--------------------------------------------------------------|
D|-x-x-8--x-x-6--x-x-6--x-x-6--x-x-6--5---------8-8-8-8-8-8-88--|
A|-x-x-8--x-x-6--x-x-6--x-x-6--x-x-6--5-ring----8-8-8-8-8-8-88--|
E|-x-x-6--x-x-4--x-x-4--x-x-4--x-x-4--3---------6-6-6-6-6-6-66--|