📖 Update README.md and add DEVELOPING.md (#31)

Author: alanorozco

DEVELOPING.md

@@ -0,0 +1,48 @@
+# Developing
+
+## Command line
+
+### Installing dependencies
+
+```console
+npm install
+```
+
+### Building
+
+```console
+npm run build
+```
+
+### Development
+
+You can watch to rebuild on every change using:
+
+```console
+npm run dev
+```
+
+To test, you may run the example Storybook:
+
+```console
+npm run storybook
+```
+
+For a manual testing workflow, you should run `dev` and `storybook` at the same time.
+
+## Testing local version elsewhere
+
+You may configure a user package (like `amphtml`) to use your locally built version by using a [package path.](https://docs.npmjs.com/cli/v7/configuring-npm/package-json#local-paths)
+
+### In [`ampproject/amphtml`](https://github.com/ampproject/amphtml/)
+
+Point to a local copy on `build-system/tasks/storybook/package.json`. The following relative path has `amphtml/` and `storybook-addon-amp/` on the same level directory:
+
+```diff
+  "devDependencies" {
+-   "@ampproject/storybook-addon-amp": "1.1.1",
++   "@ampproject/storybook-addon-amp": "file:../../../../storybook-addon-amp",
+  }
+```
+
+This way, you may use the local addon package's `npm run dev` in conjunction with `amp storybook` under `amphtml/`. Changes are picked up automatically.

README.md

@@ -30,7 +30,7 @@ module.exports = {
 An AMP story uses `withAmp` decorator:
 
 ```js
-import { h } from 'preact';
+import {h} from 'preact';
 import {storiesOf} from '@storybook/preact';
 import {withAmp} from '@ampproject/storybook-addon';
 
@@ -57,3 +57,20 @@ The following parameters can be specified:
 
 1. `extensions: [{name, version}]` - a list of extensions to be installed.
 2. `experiments: [string]` - a list of experiments to enabled.
+
+### `amp-script` hashes
+
+Inline scripts used by `amp-script` require a `<meta name="amp-script-src">` tag that includes [their content hash](https://amp.dev/documentation/components/amp-script/#calculating-the-script-hash).
+
+This addon generates the script hash for stories that need it. The following works without writing the respective `<meta>` tag:
+
+```js
+export const UsingInlineScript = () => (
+  <>
+    <amp-script script="hello" nodom></amp-script>
+    <script id="hello" type="text/plain" target="amp-script">
+      {`console.log('Hello');`}
+    </script>
+  </>
+);
+```