updated doco to use environment.yml for installing conda dependencies

these dependencies were necessary to install via conda rather than pip on macOS ARM.

doc/getting_started/installation.rst

@@ -44,7 +44,7 @@ Use the following commands to download the repo, create and activate a conda or
 
        .. code-block:: bash
 
-           conda create -n "eeg-expy" python=3.8 git pip
+           conda env create -f environment.yml -n "eeg-expy"
 
            conda activate "eeg-expy"