fix(view-on-github): Add readme and fix bug

internal_packages/message-view-on-github/README.md

@@ -0,0 +1,21 @@
+# View on GitHub
+
+The "View on GitHub" plugin adds a button to the toolbar above the message view.
+When you view a message from GitHub that contains a "View on GitHub" link,
+the button appears and makes it easy to jump to the issue / pull request / comment
+on GitHub.
+
+This example is a good starting point for plugins that want to create custom
+actions.
+
+#### Install this plugin
+
+1. Download and run N1
+
+2. From the menu, select `Developer > Install a Plugin Manually...`
+   The dialog will default to this examples directory. Just choose the
+   package to install it!
+
+   > When you install packages, they're moved to `~/.nylas/packages`,
+   > and N1 runs `apm install` on the command line to fetch dependencies
+   > listed in the package's `package.json`

internal_packages/message-view-on-github/lib/main.jsx

@@ -48,7 +48,7 @@ up or your package is manually activated.
 */
 export function activate() {
   ComponentRegistry.register(ViewOnGithubButton, {
-    role: 'MessageList:ThreadActionsToolbarButton',
+    role: 'ThreadActionsToolbarButton',
   });
 }