Add documentation about thin-min configuration

doc/ref/configuration/master.rst

@@ -746,6 +746,24 @@ authentication with minions
 
     ssh_use_home_key: False
 
+``thin_extra_mods``
+-------------------
+
+Default: None
+
+List of additional modules, needed to be included into the Salt Thin.
+Pass a list of importable Python modules that are typically located in
+the `site-packages` Python directory so they will be also always included
+into the Salt Thin, once generated.
+
+
+``min_extra_mods``
+------------------
+
+Default: None
+
+Identical as `thin_extra_mods`, only applied to the Salt Minimal.
+
 Master Security Settings
 ========================