document Canvas#registerFont in readme+example

Readme.md

@@ -170,6 +170,24 @@ canvas.toDataURL('image/jpeg', {opts...}, function(err, jpeg){ }); // see Canvas
 canvas.toDataURL('image/jpeg', quality, function(err, jpeg){ }); // spec-following; quality from 0 to 1
 ```
 
+### Canvas#registerFont for bundled fonts
+
+It can be useful to use a custom font file if you are distributing code that uses node-canvas and a specific font. Or perhaps you are using it to do automated tests and you want the renderings to be the same across operating systems regardless of what fonts they have installed.
+
+To do that, you should use `Canvas#registerFont`.
+
+**You need to call it before the Canvas is created**
+
+```javascript
+Canvas.registerFont('comicsans.ttf');
+
+var canvas = new Canvas(500, 500),
+  ctx = canvas.getContext('2d');
+
+ctx.font = '12px "Comic Sans"';
+ctx.fillText(250, 10, 'Everyone hates this font :(');
+```
+
 ### CanvasRenderingContext2d#patternQuality
 
 Given one of the values below will alter pattern (gradients, images, etc) render quality, defaults to _good_.

examples/font.js

@@ -11,6 +11,10 @@ function fontFile(name) {
   return path.join(__dirname, '/pfennigFont/', name);
 }
 
+// Pass each font, including all of its individual variants if there are any, to
+// `registerFont`. When you set `ctx.font`, refer to the styles and the family
+// name as it is embedded in the TTF. If you aren't sure, open the font in
+// FontForge and visit Element -> Font Information and copy the Family Name
 Canvas.registerFont(fontFile('Pfennig.ttf'));
 Canvas.registerFont(fontFile('PfennigBold.ttf'));
 Canvas.registerFont(fontFile('PfennigItalic.ttf'));