Update README.md

## Dependencies

Compiler (C++11): GNU 5+, Clang 8+

CMake 3.9+

```

Compiler (C++14): GNU 6.1+, Clang 3.4+

CMake 3.9+ (for build)

XACC: see https://xacc.readthedocs.io/en/latest/install.html#building-xacc

## Build instructions

For CMake 3.9+, do not use the apt-get installer, instead use `pip`, and

ensure that `/usr/local/bin` is in your PATH:

clang-dev version 8+

```

## Linux Build Instructions

Easiest way to install CMake - do not use the package manager, 

instead use `pip`, and ensure that `/usr/local/bin` is in your PATH:

```bash

$ python -m pip install --upgrade cmake

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

```

On Ubuntu 16.04 (for others, replace xenial with Ubuntu release name), 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-9 main" > /etc/apt/sources.list.d/llvm.list

$ apt-get update

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

$ apt-get update && 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

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

```

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

$ cd qcor

$ mkdir build && cd build

$ cmake .. -DXACC_DIR=~/.xacc (or wherever you installed XACC) 

$ [with tests] cmake .. -DXACC_DIR=~/.xacc -DQCOR_BUILD_TESTS=TRUE 

$ make install

```

Update your PATH to ensure that the ```qcor``` compiler is available.

```bash

$ export PATH=$PATH:$HOME/.xacc/bin

$ export PATH=$PATH:$HOME/.xacc/bin (or wherever you installed XACC)

```

## Example Usage

}

```

To compile this with QCOR, run the following

To compile this with QCOR targeting the TNQVM simulator, run the following

```bash

$ qcor -o deuteron deuteron.cpp

$ qcor -o deuteron -a tnqvm deuteron.cpp

```

This will create the ```deuteron``` quantum-classical binary executable.

Now just run

```bash

$ ./deuteron --accelerator tnqvm

$ ./deuteron 

```