Add README for Message Icons usage instructions

This README provides instructions for adding custom icons to the message display app.

Author: RKBoss6

apps/messageicons/README.md

@@ -0,0 +1,10 @@
+# Message Icons
+Provides icons for phone apps that are utilized by `message gui` and any other message display app. 
+
+## Adding your own icons
+- Clone the repo on your local machine, if you haven't done so already.
+- Locate the image you want to use as an icon. Make sure it is 24x24px, and has a black foreground and transparent background (you can color the foreground one color only later on)
+- Upload it to the `icons` folder in the `messageicons` folder.
+- Add your app name and the corresponding image you added to the `icon_names.json` file
+- Run the `generate.js` script. Be sure you have the `png-js` dependency needed. (you can install it by running `npm install png-js` in the terminal)
+- Once finished generating, navigate to the `lib.js` file, and add the color for your foreground and the corresponding app.