add wrap info to readme

Author: timhaywood

README.md

@@ -25,14 +25,14 @@ npm install rollup-plugin-ae-jsx --save-dev
 Create a `rollup.config.js` [configuration file](https://www.rollupjs.org/guide/en/#configuration-files), import the plugin, and add it to the `plugins` array:
 
 ```js
-import afterEffectJsx from "./rollup-plugin-ae-jsx";
-import pkg from "./package.json";
+import afterEffectJsx from './rollup-plugin-ae-jsx';
+import pkg from './package.json';
 
 export default {
-  input: "src/index.ts",
+  input: 'src/index.ts',
   output: {
-    file: "dist/index.jsx",
-    format: "es",
+    file: 'dist/index.jsx',
+    format: 'es',
   },
   external: Object.keys(pkg.dependencies),
   plugins: [afterEffectJsx()],
@@ -44,13 +44,86 @@ export default {
 
 Then call `rollup` either via the [CLI](https://www.rollupjs.org/guide/en/#command-line-reference) or the [API](https://www.rollupjs.org/guide/en/#javascript-api).
 
-## Proccess
+## Options
+
+### `wrap`
+
+Type: `boolean` \
+Default: `false`
+
+Wraps compiled code in a `get()` function. See [Wrapping](#wrapping) for more detail.
+
+## Process
 
 1. Creating a list of the exported functions and variables from the index file
 2. Removing non-compatible statements: `['ExpressionStatement', 'DebuggerStatement', 'ImportDeclaration', 'ExportNamedDeclaration'];`
 3. Converting function and variable declarations into `.jsx` compliant syntax
 4. Wrapping in braces (`{}`)
 
+## Wrapping
+
+Compiling code that references top level functions or variables will error when run in After Effects, since each exported property is isolated from the surrounding code.
+
+For example the following source code:
+
+```js
+function add(a, b) {
+  return a + b;
+}
+
+function getFour() {
+  return add(2, 2);
+}
+
+export { add, getFour };
+```
+
+Will compile to the following `.jsx` file:
+
+```js
+{
+  add(a, b) {
+    return a + b;
+  },
+  getFour() {
+    return add(2, 2); // error, add is not defined
+  }
+}
+```
+
+Which will error, since `add()` is not defined within the scope of `getFour()`.
+
+This can be solved by wrapping all of your code in a parent function, which `rollup-plugin-jsx` will do for you if `wrap` is set to true.
+
+```js
+// rollup.config.js
+plugins: [afterEffectJsx({ wrap: true })],
+```
+
+The compiled `.jsx` would then be:
+
+```js
+{
+  get() {
+    function add(a, b) {
+      return a + b;
+    }
+
+    function getFour() {
+      return add(2, 2);
+    }
+
+    return { add, getFour }
+  }
+}
+```
+
+You then would need to call `.get()` in your expressions:
+
+```js
+const { getFour, add } = footage('index.jsx').sourceData.get();
+```
+
 ## Meta
 
 [CONTRIBUTING](/.github/CONTRIBUTING.md)