(docs): add a section on bundler performance optimizations

- this is likely an area of concern for users and may even be a
  barrier to adoption for this library, so document it directly in
  the README to reach the greatest amount of people
  - some users may not even know these optimizations exist, so this
    should particularly help them in getting up to speed (pun intended)

- major downside of documenting this officially is that it must now be
  supported / maintained -- namely, this means that changing the path
  to ammo.js would now be considered a breaking change
  - but this library doesn't go through many changes and all that
    physijs code has been split into its own directory, so that's a
    trade-off I'm willing to make

README.md

@@ -52,6 +52,53 @@ npm install -D webworkify
 
 See the [webpack.js](webpack.js) and [browserify.js](browserify.js) files for examples as to how one might configure for a different bundler.
 
+## Bundler Performance Optimizations
+
+**Please note**: this section is entirely _optional_, it is only for advanced users and not necessary to use this library.
+
+Using `physijs-webpack` may bulk up your bundle by quite a bit, primarily because `physijs` depends on `ammo.js`, which is roughly ~1.2MB (minified) alone.
+While caching of repeated builds will certainly speed up performance by quite a bit, we can use some other optimizations to further improve your bundler's performance.
+
+### noParse
+
+One of these is the `noParse` config option ([webpack](https://webpack.js.org/configuration/module/#modulenoparse)|[browserify](https://github.com/browserify/browserify#usage)) that instructs the bundler to skip parsing of certain files and is usually used as an optimization for large files (like `ammo.js`!).
+
+With `webpack`, this optimization might look like:
+
+```javascript
+// ...
+module.exports = {
+  // ...
+  module: {
+    // don't parse ammo
+    noParse: require.resolve('physijs-webpack/physijs/vendor/ammo.js')
+  },
+  // ...
+}
+```
+
+And with the [`browserify` API](https://github.com/browserify/browserify#browserifyfiles--opts), this optimization might look like:
+
+```javascript
+const browserify = require('browserify')
+// ...
+
+browserify({
+  // ...
+  // don't parse ammo
+  noParse: [require.resolve('physijs-webpack/physijs/vendor/ammo.js')],
+  // ...
+})
+```
+
+### other optimizations
+
+If you are looking to speed up your build even further, you may want to look into configuring `externals` ([webpack](https://webpack.js.org/configuration/externals/)|[browserify](https://github.com/browserify/browserify#bexternalfile)) (and possibly configuring `ignore`s ([webpack](https://webpack.js.org/plugins/ignore-plugin/)|[browserify](https://github.com/browserify/browserify#bignorefile))).
+
+You may also want to apply these same bundler performance optimizations to `three` as well, as it is also a fairly large library.
+
+Please send a PR if you identify any other performance optimizations that you think may be useful to others!
+
 ## Credits
 
 Thanks to @silviopaganini for creating the [initial browserify version](https://github.com/silviopaganini/physijs-browserify)!