update docs to include import of countries which is necessary to be able to import addresses

docs/source/installation/load-addresses.rst

@@ -8,6 +8,16 @@ Chill can store a list of geolocated address references, which are used to sugge
 
 Those addresses may be load from a dedicated source.
 
+Countries
+=========
+
+In order to load addresses into the chill application we first have to make sure that a list of countries is present.
+To import the countries run the following command.
+
+.. code-block:: bash
+
+    bin/console chill:main:countries:populate
+
 In France
 =========