Add watchify recipe

Offers considerably faster browserify builds by using the
watchify module and vinyl-source-stream in place of
gulp-browserify.

docs/recipes/fast-browserify-builds-with-watchify.md

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+# Fast browserify builds with watchify
+
+As a [browserify](http://github.com/substack/node-browserify) project begins to
+expand, the time to bundle it slowly gets longer and longer. While it might
+start at 1 second, it's possible to be waiting 30 seconds for your project to
+build on particularly large projects.
+
+That's why [substack](http://github/substack) wrote
+[watchify](http://github.com/substack/watchify), a persistent browserify
+bundler that watches files for changes and *only rebuilds what it needs to*.
+This way, that first build might still take 30 seconds, but subsequent builds
+can still run in under 100ms – which is a huge improvement.
+
+Watchify doesn't have a gulp plugin, but it doesn't need one either: you can
+use [vinyl-source-stream](http://github.com/hughsk/vinyl-source-stream) to pipe
+the bundle stream into your gulp pipeline.
+
+``` javascript
+var source = require('vinyl-source-stream')
+var watchify = require('watchify')
+var gulp = require('gulp')
+
+var bundler = watchify('./src/index.js')
+var watchFiles = [
+  './src/**/*.js',
+  './src/*.js'
+]
+
+gulp.task('browserify', function() {
+  return bundler.bundle()
+    .pipe(source('bundle.js'))
+    .pipe(gulp.dest('./dist'))
+})
+
+gulp.task('watch', ['browserify'], function() {
+  gulp.watch(watchFiles, ['browserify'])
+})
+
+// Optionally, you can apply transforms
+// and other configuration options on the
+// bundler just as you would with browserify
+bundler.transform('brfs')
+```