Readme "Compile LLVM yourself:" contains wrong steps

[elix22]

At least in my case the right step that compiled successfully:
git clone https://github.com/llvm/llvm-project.git
~$ cd llvm-project
llvm-project$ git checkout release/17.x
llvm-project$ mkdir llvm/build
llvm-project$ cd llvm/build
build$ cmake .. -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS="clang"
build$ make