re-adding system example

Author: rachoac

examples/position_logger_component/dist/index.d.ts

@@ -47,7 +47,7 @@ export declare abstract class ComponentWrapper<SCHEMA = {}, SYSTEM extends AFram
 }
 export declare abstract class SystemWrapper<SCHEMA extends {
     [key: string]: any;
-}> implements AFrame.System {
+} = {}> implements AFrame.System {
     data: SCHEMA;
     schema: AFrame.Schema<SCHEMA>;
     name: string;

examples/position_logger_component/dist/index.map

@@ -0,0 +1,15 @@
+# Sphere Registry A-Frame System
+
+This is a complete example of a how to create an A-Frame system using `SystemWrapper`. You can see it in action by simply opening `index.html` in a browser. Spheres that have been aded to the screen are being tracked by the `sphere-regsitry` system. The latter records sphere entities registered with it onto a textbox visible on the left side of the screen.
+
+You can click the link at the top of the page to add more spheres; watch the sphere registry text change as you add more spheres.
+
+# Building the example
+
+1. `yarn install` to install the dependencies.
+
+2. `yarn build` to create CDN publishable artifacts in the `dist-umd` folder.
+
+# Making the component globally useable
+
+Exposing `dist-umd` via a CDN such as rawgit or jsdelivr will make it easy for 3rd party developers to use systems such as the sphere registry.