docs: 📝 add docs around adding helpers.

README.md

@@ -1,3 +1,38 @@
 # Downpour
 
-Sparkbox implementation of [drizzle-builder](https://www.npmjs.com/package/drizzle-builder)
+Sparkbox implementation of [drizzle-builder][db]
+
+
+## Usage
+
+Downpour exposes the [drizzle-builder][db] as a function to compile handlebars templates into HTML.
+
+All [drizzle-builder options](https://github.com/cloudfour/drizzle-builder#options) are valid.
+
+Downpour includes a few handlebars helpers by default:
+
+- all [@cloudfour/hbs-helpers](https://github.com/cloudfour/core-hbs-helpers/tree/master/lib)
+- [ifProd](https://github.com/sparkbox/ifProd-helper)
+- [is][assemble]
+- [isn't][assemble]
+- [split][assemble]
+
+To add additional helpers create a `helpers` key in the options object like so:
+
+``` javascript
+const downpour = require('downpour');
+const { myHelperFunc } = require('my-helper-package');
+
+const opts = {
+  helpers: {
+    myHelper: myHelperFunc,
+  },
+};
+
+downpour(opts, cb);
+
+```
+
+
+[db]: https://www.npmjs.com/package/drizzle-builder
+[assemble]: https://github.com/helpers/handlebars-helpers

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@sparkbox/downpour",
-  "version": "0.0.9",
+  "version": "0.0.10",
   "description": "Sparkbox implementation of drizzle-builder",
   "engines": {
     "node": ">=6.9.1"