Merge pull request #385 from KristjanESPERANTO/functions

docs(introduction): clarify usage of functions in config.js for browser availability

Author: sdetweil

configuration/introduction.md

@@ -19,6 +19,9 @@
        },
      ],
    };
+
+   /*************** DO NOT EDIT THE LINE BELOW ***************/
+   if (typeof module !== "undefined") {module.exports = config;}
    ```
 
    See [module configuration](/modules/configuration) for more information and
@@ -96,6 +99,11 @@ debugging:
   server security header behavior.
 - `hideConfigSecrets` is documented in detail in [Secrets](./secrets).
 
+When you use functions in `config.js`, keep them inside the exported `config`
+object if they need to be available in the browser. MagicMirror² serves the
+browser copy of the configuration from the `config` object, so free-standing
+helper functions outside that object are not included there.
+
 #### Bash Environment variables
 
 There are two environment variables that override part or all of config.js. They