A little bug in the file format.md

[thuliu-yt16]

Recently, I am interested in Thistlethwaite Method so I searched it in github and found the repository. Thank you for sharing your idea and code.

When I tried to find out how you use values of type vector to represent different cube states, I opened the file "format.md" and read it. But the second paragraph made me confused. Obviously, performing U, a solved cube cannot be LF UR UB UL RF DR DB DL FU FD BR BL LFU URB UBL LDF RUF RFD DLB DBR because UR should locate at Position 0 rather than LF. Finally, I noticed your explanation about U and confirmed that it should be a F instead of a U.

So please fix the bug. Thank you. :D