Update readme.md
Update readme.md

Adding some notes about how to generate multires images ^_^ (it took me some time to figure it out hehe). 

Thanks by the way for this lib! I love it :D
mpetroff/pannellum,mpetroff/pannellum,eric-seekas/pannellum,ywjrg/pannellum,ywjrg/pannellum,riuson/pannellum,quentinyang/pannellum,quentinyang/pannellum,mpetroff/pannellum,Benvii/pannellum,psteph801/psteph801.github.io,Benvii/pannellum,eric-seekas/pannellum,riuson/pannellum,eric-seekas/pannellum,ywjrg/pannellum,psteph801/psteph801.github.io,riuson/pannellum,Benvii/pannellum,psteph801/psteph801.github.io,quentinyang/pannellum,ywjrg/pannellum,quentinyang/pannellum,Benvii/pannellum,riuson/pannellum,psteph801/psteph801.github.io,eric-seekas/pannellum,mpetroff/pannellum