Update README.md

Adds a bit more information to the README

README.md

@@ -26,6 +26,40 @@ ctx.fillRect(100,100,100,100);
 const mySerializedSVG = ctx.getSerializedSvg(); 
 ```
 
+Wrapping canvas elements:
+
+```javascript
+import { Context, Element } from 'svgcanvas';
+
+const canvas = document.createElement("canvas");
+const context2D = canvas.getContext("2d");
+
+// more options to pass into constructor:
+const options = {
+	height: 2000, // falsy values get converted to 500
+	width: 0 / 0, // falsy values get converted to 500
+	ctx: context2D, // existing Context2D to wrap around
+	enableMirroring: false, // whether canvas mirroring (get image data) is enabled (defaults to false)
+	document: undefined, // overrides default document object
+}
+
+// Creates a mock canvas context (mocks `context2D` above)
+const ctx = new Context(options);
+
+// draw your canvas like you would normally
+ctx.fillStyle = "red";
+ctx.fillRect(100, 100, 100, 100);
+
+ctx.getSerializedSvg(); // returns the serialized SVG
+ctx.getSvg(); // returns the inline svg element
+
+// Creates a mock canvas element (mocks `canvas` above)
+const dom = new Element(options);
+dom.ctx; // the internal context, via `new Context(options)`
+dom.wrapper; // a div with the svg as a child
+dom.svg; // the inline svg element
+```
+
 ## Tests
 
 https://zenozeng.github.io/p5.js-svg/test/