switch install docs to use mamba (#223)

docs/install.rst

@@ -1,10 +1,21 @@
 Installation
 ============
 
-conda
+mamba
 -----
 
-Install espaloma::
+We recommend using `mamba <https://mamba.readthedocs.io/en/latest/mamba-installation.html#mamba-installation>`_ which is a drop-in replacement for ``conda`` and is much faster.
 
-    conda install -c conda-forge "espaloma=0.3.2"
+.. code-block:: bash
 
+   $ mamba create --name espaloma -c conda-forge "espaloma=0.3.2"
+
+Note: If you are using a Mac with an M1/M2 chip, you will need to install and run ``espaloma`` using `Rosetta <https://support.apple.com/en-us/HT211861>`_ by using the following commands:
+
+.. code-block:: bash
+
+   CONDA_SUBDIR=osx-64 mamba create --name espaloma -c conda-forge "espaloma=0.3.2"
+   mamba activate espaloma
+   mamba config --env --set subdir osx-64
+
+This will ensure that any other packages installed in the ``espaloma`` environment will also use Rosetta.