Update README.md

$ export PATH=$PATH:/usr/local/bin

```

On Ubuntu 16+, install latest clang and llvm libraries and headers (you may need sudo)

On Ubuntu 16.04 (for others, replace xenial with Ubuntu release name), install latest clang and llvm libraries and headers (you may need sudo)

```bash

$ wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -

$ echo "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial main" > /etc/apt/sources.list.d/llvm.list

$ echo "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-9 main" > /etc/apt/sources.list.d/llvm.list

$ apt-get update

$ apt-get install -y libclang-9-dev llvm-9-dev

$ apt-get install -y libclang-9-dev llvm-9-dev clangd-9

$ ln -s /usr/bin/llvm-config-9 /usr/bin/llvm-config

$ (for theia) ls -s /usr/bin/clangd-9 /usr/bin/clangd

```

Note that, for now, developers must clone QCOR manually: