Add details about button plugin configuration

Author: adamwathan

README.md

@@ -31,16 +31,78 @@ In `plugins/object-fit/index.js` you'll find an example of a plugin that adds a
 The only option it exposes are the variants you'd like to generate (`responsive`, `hover`, `focus`, etc.), which you pass to the plugin as a simple array:
 
 ```js
-plugins: {
+module.exports = {
+  // ...
+
+  plugins: [
     // ...
     require('./plugins/object-fit')(['responsive']),
+  ],
 }
 ```
 
 This is just about the simplest type of plugin you could make.
 
 ## Simple Buttons
 
-In `plugins/simple-buttons/index.js` you'll find an example of a plugin that adds new component classes.
+In `plugins/simple-buttons/index.js` you'll find an example of a plugin that adds new button component classes.
 
 ![](https://user-images.githubusercontent.com/4323180/37477287-b367cf88-284d-11e8-823b-f793c3ba1119.png)
+
+This plugin exposes quite a number of configuration options *(all optional)*, which can be passed to the plugin as an object:
+
+```js
+module.exports = {
+  // ...
+
+  plugins: [
+    // ...
+    require('./plugins/simple-buttons')({
+
+
+      // Set some default styles for all buttons.
+      borderRadius: '.25rem',   // Default: .25rem
+      fontWeight: '600',        // Default: 600
+      lineHeight: '1.25',       // Default: 1.25
+      fontSize: '1rem',         // Default: 1rem
+      padding: '.5rem 1rem',    // Default: .5rem 1rem
+
+
+      // Specify the button colors you'd like to generate.
+      // 
+      // By default, buttons are generated for all of Tailwind's
+      // default base colors.
+      colors: {
+        // Class name: `.btn-primary`
+        primary: {
+          background: colors['blue'],
+          text: colors['white'],
+        },
+        // Class name: `.btn-secondary`
+        secondary: {
+          background: colors['grey'],
+          text: colors['black'],
+        },
+      },
+
+
+      // Specify additional button sizes you'd like to generate.
+      // 
+      // You can override any of the default styles from above
+      // at any given button size.
+      sizes: {
+        sm: {
+          fontSize: '.875rem',
+          padding: '.5rem .75rem',
+        },
+        lg: {
+          fontSize: '1.25rem',
+          padding: '.75rem 1.5rem',
+          borderRadius: '.5rem',
+        }
+      }
+    }),
+  ],
+}
+```
+