Updated TopBar buttons doc page

docs/docs/topBar-buttons.md

@@ -57,3 +57,34 @@ Navigation.push(this.props.componentId, {
   }
 }
 ```
+
+# Modifying buttons at runtime
+
+As buttons are part of a screen's options, they can be modified like any other styling option using the `mergeOptions` command.
+
+## Setting buttons
+The following command will set the screen's right buttons. If the screen already has Right Buttons declared - they will be overridden.
+
+```js
+Navigation.mergeOptions(this.props.componentId, {
+  topBar: {
+    rightButtons: [
+      {
+        id: 'myDynamicButton',
+        title: 'My Button'
+      }
+    ]
+  }
+});
+```
+
+## Removing buttons
+Buttons can be removed by setting zero buttons as shown in the snippet below.
+
+```js
+Navigation.mergeOptions(this.props.componentId, {
+  topBar: {
+    rightButtons: []
+  }
+});
+```