examples: Add comments for ring example

examples/ring/main.pony

@@ -1,3 +1,42 @@
+"""
+A ring is a group of processes connected to each other using
+unidirectional links through which messages can pass from process to
+process in a cyclic manner.
+
+The logic of this program is as follows:
+* Each process in a ring is represented by the actor `Ring`
+* `Main` creates Ring by instantiating `Ring` actors based on the
+  arguments passed and links them with each other by setting the next
+  actor as the previous ones number and at the end linking the last actor
+  to the first one thereby closing the links and completing the ring
+* Once the ring is complete messages can be passed by calling the `pass`
+  behaviour on the current `Ring` to its neighbour.
+* The program prints the id of the last `Ring` to receive a message
+
+For example if you run this program with the following options `--size 3`
+and `--pass 2`. It will create a ring that looks like this:
+
+
+        *  *              *  *
+     *        *        *        *
+    *     1    *_ _ _ *     2    *
+    *          *      *          *
+     *        *        *        *
+        *  *              *  *
+          \                 /
+           \               /
+            \             /
+             \    *  *   /
+               *        *
+              *     3    *
+              *          *
+               *        *
+                  *  *
+
+and print 3 as the id of the last Ring actor that received the
+message.
+"""
+
 use "collections"
 
 actor Ring