fix: docs plugin explanation

docs/user_guide/plugin_system.rst

@@ -20,7 +20,7 @@ visualize how the different classes are connected and composed with **OpenVarian
 |
 
 As we have mentioned before, the plugin has to be present on the `annotation` file in order to be used. Custom plugins will be placed in the 
-folder where the environment variable `OPENVAR_PLUGIN` points (`/home/user/.local/openvariant/` by default). 
+folder where the environment variable :bash:`OPENVAR_PLUGIN` points (:bash:`/home/user/.local/openvariant/` by default). 
 The `Builder` will manage to find them and apply the data transformation.
 Plugins will inherit `Context` and `Plugin` as base classes for each plugin. These classes are described as it follows: