Update the project name in README.txt

Per llvm.org: "The name "LLVM" itself is not an acronym; it is the full
name of the project."

Differential Revision: https://reviews.llvm.org/D47796

llvm-svn: 334087
GitOrigin-RevId: 86026bdaee77c40009bdb91d9543bdc679b792ea
1 file changed