Dial: add contents to documentation

Author: thyttan

modules/Dial.md

@@ -1,4 +1,60 @@
-Dial Library
-============
+Bangle.js Dial Library
+======================
 
+> Take a look at README.md for hints on developing with this library.
 
+Usage
+-----
+
+```JS
+var Dial = require("Dial");
+var dial = new Dial(cb, options)
+Bangle.on("drag", dial);
+
+or
+
+var dial = require("Dial")(cb, options);
+Bangle.on("drag", dial);
+```
+
+For example:
+
+```JS
+let cb = (plusOrMinusOne)=>{print(plusOrMinusOne)};
+let options = {
+  stepsPerWholeTurn : 6,
+  dialRect : {
+    x: 0,
+    y: 0,
+    w: g.getWidth()/2,
+    h: g.getHeight()/2,
+  }
+}
+
+let dial = require("Dial")(cb, options);
+Bangle.on("drag", dial);
+```
+
+`cb` (first argument) is a callback function that should expect either `+1` or `-1` as argument when called.
+
+`options` (second argument) (optional) is an object containing:
+
+stepsPerWholeTurn - how many steps there are in one complete turn of the dial.
+dialRect - decides the area of the screen the dial is set up on.
+
+Defaults:
+```js
+{ stepsPerWholeTurn : 7
+  dialRect : {
+    x: 0,
+    y: 0,
+    w: g.getWidth(),
+    h: g.getHeight(),
+  },
+}
+```
+
+Notes
+-----
+
+A complementary library for drawing graphics for the dial would be neat and is being considered.