gh-pages installation formatting fix 2

Author: marufr

docs/source/ch04_installation.rst

@@ -220,6 +220,7 @@ Instructions for installing `mamba` can be found
 
 Installation option #1 (necesary for Windows):
 
+.. code-block:: bash
 
     mamba env create -f ./installation/sira_env.yml
     mamba activate sira_env
@@ -229,6 +230,8 @@ Installation option #1 (necesary for Windows):
 
 Installation option #2 (for Linux workstations, needs to be adapted for HPC env):
 
+.. code-block:: bash
+
     sudo apt-get update
     grep -vE '^\s*#|^\s*$' ./installation/packagelist_linux.txt | \
     xargs -r sudo apt-get install -y --no-install-recommends