Update docs to reflect that LLVM 8 / clang 8 work fine
Update docs to reflect that LLVM 8 / clang 8 work fine

lgritz/OpenShadingLanguage,lgritz/OpenShadingLanguage,lgritz/OpenShadingLanguage,aconty/OpenShadingLanguage,aconty/OpenShadingLanguage,brechtvl/OpenShadingLanguage,brechtvl/OpenShadingLanguage,aconty/OpenShadingLanguage,imageworks/OpenShadingLanguage,brechtvl/OpenShadingLanguage,lgritz/OpenShadingLanguage,aconty/OpenShadingLanguage,brechtvl/OpenShadingLanguage,imageworks/OpenShadingLanguage,brechtvl/OpenShadingLanguage,aconty/OpenShadingLanguage,lgritz/OpenShadingLanguage,imageworks/OpenShadingLanguage,imageworks/OpenShadingLanguage,imageworks/OpenShadingLanguage