Improve README section on customization

Dockerfile

@@ -28,13 +28,15 @@ RUN pip3 install notebook ipywidgets  && \
 # install Appmode
 COPY . /opt/appmode
 WORKDIR /opt/appmode/
-RUN pip3 install .                                            && \
+RUN pip3 install .                                           && \
     jupyter nbextension     enable --py --sys-prefix appmode && \
     jupyter serverextension enable --py --sys-prefix appmode
 
-# Uncomment following RUN line to hide the "Edit App" button.
-# Beware that this does not prevent users from changing the URL manually.
-# RUN mkdir -p ~/.jupyter/custom/ && echo "\$('#appmode-leave').hide();" >> ~/.jupyter/custom/custom.js
+# Possible Customizations
+# RUN mkdir -p ~/.jupyter/custom/                                          && \
+#     echo "\$('#appmode-leave').hide();" >> ~/.jupyter/custom/custom.js   && \
+#     echo "\$('#appmode-busy').hide();"  >> ~/.jupyter/custom/custom.js   && \
+#     echo "\$('#appmode-loader').append('<h2>Loading...</h2>');" >> ~/.jupyter/custom/custom.js
 
 # Launch Notebook server
 EXPOSE 8888

README.md

@@ -33,14 +33,6 @@ dependencies:
   - appmode
 ```
 
-## Hidding the edit button
-
-In some cases it might be useful to hide the _Edit App_ button. This can be achieved by adding in the following line to the [custom.js](http://jupyter-notebook.readthedocs.io/en/stable/examples/Notebook/JavaScript%20Notebook%20Extensions.html#custom.js) file:
-```
-$('#appmode-leave').hide();
-```
-Beware that users can still leave Appmode by changing the URL manually.
-
 ## Description
 
 Appmode consist of a server-side and a notebook extension for Jupyter. Together these two extensions provide the following features:
@@ -53,6 +45,16 @@ Appmode consist of a server-side and a notebook extension for Jupyter. Together
 
 - To allow for passing information between notebooks via url parameters, the current url is injected into the variable ``jupyter_notebook_url``.
 
+## Customization
+
+The UI elements of Appmode can be customized via the [custom.js](http://jupyter-notebook.readthedocs.io/en/stable/examples/Notebook/JavaScript%20Notebook%20Extensions.html#custom.js) file. Some examples are:
+```
+$('#appmode-leave').hide();                          // Hides the edit app button.
+$('#appmode-busy').hide();                           // Hides the kernel busy indicator.
+$('#appmode-loader').append('<h2>Loading...</h2>');  // Adds a loading message.
+```
+Beware that hiding the edit button does not prevent users from leaving Appmode by changing the URL manually.
+
 ## Development
 
 With the included [Dockerfile](./Dockerfile) a development environment can be quickly created: