add basic information to README.md

Author: kbatten

README.md

@@ -1,2 +1,42 @@
 httpcanvas
 ==========
+
+write to an html5 canvas using go
+
+The `app` function starts once a we browser connects to `http://host:port/`
+
+That request downloads a bit of html and javascript to connect to the server and run commands
+
+Further GET requests causes the output to move to the most recent request.
+
+## Example
+``` go
+package main
+
+import (
+    "github.com/kbatten/httpcanvas"
+    "math"
+    "time"
+)
+
+func app(context *httpcanvas.Context) {
+    centerX := context.Width / 2
+    centerY := context.Height / 2
+
+    context.BeginPath()
+    context.Arc(centerX, centerY, 70, 0, 2*math.Pi, false)
+    context.FillStyle("green")
+    context.Fill()
+
+    time.Sleep(5 * time.Second)
+
+    context.LineWidth(5)
+    context.StrokeStyle("#003300")
+    context.Stroke()
+}
+
+func main() {
+    httpcanvas.ListenAndServe(":8080", app)
+}
+
+```