update cpu install step

README.md

@@ -53,15 +53,15 @@ Additional notebooks in [notebooks](notebooks) demonstrate other aspects of the
 
 PySCF on IPU requires Python 3.8, [JAX IPU experimental](https://github.com/graphcore-research/jax-experimental), [TessellateIPU library](https://github.com/graphcore-research/tessellate-ipu) and [Graphcore Poplar SDK 3.2](https://www.graphcore.ai/downloads).
 
-We recommend upgrading `pip` to the latest stable release to prepare your enviroment.
+We recommend upgrading `pip` to the latest stable release to prepare your environment.
 ```bash
 pip install -U pip
 ```
 
 This project is currently under active development. 
 For CPU simulations, we recommend installing `pyscf-ipu` from latest `main` branch as:
 ```bash
-pip install pyscf-ipu@git+https://github.com/graphcore-research/pyscf-ipu
+pip install pyscf-ipu[cpu]@git+https://github.com/graphcore-research/pyscf-ipu
 ```
 
 and on IPU equipped machines:
@@ -128,4 +128,4 @@ Please use the following citation for the pyscf-ipu project:
   booktitle={Thirty-seventh Conference on Neural Information Processing Systems Datasets and Benchmarks Track},
   year={2023}
 }
-```
+```