add plugin option examples to docs

docs/docs/plugins.md

@@ -35,4 +35,36 @@ module.exports = {
 };
 ```
 
-Plugins can take options. Note that plugin options will be stringified by Gatsby, so they cannot be functions.
+Plugins can take options. Examples:
+
+```javascript
+module.exports = {
+  plugins: [
+    'gatsby-plugin-react-helmet',
+    {
+      // standard plugin with options example
+      resolve: `gatsby-source-filesystem`,
+      options: {
+        path: `${__dirname}/src/data/`,
+        name: 'data',
+      },
+    },
+    { 
+      resolve: 'gatsby-plugin-offline', 
+      // blank options, equivalent to string-only plugin
+      options: {
+        plugins: [], 
+      },
+    },
+    {
+      resolve: `gatsby-transformer-remark`,
+      options: {
+        // plugins inside plugins, why not
+        plugins: [`gatsby-remark-smartypants`], 
+      },
+    },
+  ],
+}
+```
+
+Note that plugin options will be stringified by Gatsby, so they cannot be functions.