Add Setup and Extending top level navs

Summary: Distinguish between integrating flipper, and developing plugins.

Reviewed By: passy

Differential Revision: D15148448

fbshipit-source-id: 7c772fa1cea7d5ed789a984039afc37bc0b8a927

docs/extending/send-data.md

@@ -0,0 +1,49 @@
+---
+id: send-data
+title: Sending Data to Plugins
+---
+
+It is often useful to get an instance of a Flipper plugin to send data to it. Flipper makes this simple with built-in support.
+
+Plugins should be treated as singleton instances as there can only be one `FlipperClient` and each `FlipperClient` can only have one instance of a certain plugin. The Flipper API makes this simple by offering a way to get the current client and query it for plugins.
+
+Plugins are identified by the string that their identifier method returns, in this example, "MyFlipperPlugin":
+
+### Android
+
+```java
+final FlipperClient client = AndroidFlipperClient.getInstance(context);
+// Client may be null if AndroidFlipperClient.createInstance() was never called
+// which is the case in production builds.
+if (client != null) {
+  final MyFlipperPlugin plugin = client.getPluginByClass(MyFlipperPlugin.class);
+  plugin.sendData(myData);
+}
+```
+
+### iOS
+
+```objective-c
+FlipperClient *client = [FlipperClient sharedClient];
+MyFlipperPlugin *myPlugin = [client pluginWithIdentifier:@"MyFlipperPlugin"];
+[myPlugin sendData:myData];
+```
+
+### C++
+
+```c++
+auto &client = FlipperClient::instance();
+
+// "MyFlipperPlugin is the return value of MyFlipperPlugin::identifier()
+auto aPlugin = client.getPlugin("MyFlipperPlugin");
+
+// aPlugin is a std::shared_ptr<FlipperPlugin>. Downcast to expected type.
+auto myPlugin = std::static_pointer_cast<MyFlipperPlugin>(aPlugin);
+
+// Alternatively, use the templated version
+myPlugin = client.getPlugin<MyFlipperPlugin>("MyFlipperPlugin");
+
+myPlugin->sendData(myData);
+```
+
+Here, `sendData` is an example of a method that might be implemented by the Flipper plugin.