Added a lengthy comment on the LLVM to Gen IR translation
Added a lengthy comment on the LLVM to Gen IR translation

zhenyw/beignet,wdv4758h/beignet,ignatenkobrain/beignet,wdv4758h/beignet,zhenyw/beignet,ignatenkobrain/beignet,freedesktop-unofficial-mirror/beignet,zhenyw/beignet,freedesktop-unofficial-mirror/beignet,zhenyw/beignet,ignatenkobrain/beignet,wdv4758h/beignet,wdv4758h/beignet,freedesktop-unofficial-mirror/beignet,ignatenkobrain/beignet,zhenyw/beignet,freedesktop-unofficial-mirror/beignet,wdv4758h/beignet,ignatenkobrain/beignet