Update README.md

Update now Compile With PPU GIT (LLVM)
Support FCTID/FCTIW instructions
Merge pull request #849 from raven02/patch-3

Support FCTID/FCTIW instructions
Merge pull request #848 from Dante38490/patch-1

Update README.md
Stub DCBI instruction
Merge pull request #850 from raven02/patch-4

Stub DCBI instruction