docs: add additional details

Adapted from:

- https://socket.io/docs/v3/client-initialization/
- https://socket.io/docs/v3/client-socket-instance/

Author: darrachequesne

README.md

@@ -12,11 +12,7 @@ See also:
 ## Table of content
 
 - [Compatibility](#compatibility)
-- [Installation](#installation)
-  - [Maven](#maven)
-  - [Gradle](#gradle)
-- [Usage](#usage)
-- [Features](#features)
+- [Documentation](#documentation)
 - [License](#license)
 
 ## Compatibility
@@ -27,180 +23,11 @@ See also:
 | 1.x    | 2.x |
 | 2.x    | 3.x |
 
-## Installation
-The latest artifact is available on Maven Central.
+## Documentation
 
-### Maven
-Add the following dependency to your `pom.xml`.
+The documentation can be found [here](https://socketio.github.io/socket.io-client-java/installation.html).
 
-```xml
-<dependencies>
-  <dependency>
-    <groupId>io.socket</groupId>
-    <artifactId>socket.io-client</artifactId>
-    <version>2.0.0</version>
-  </dependency>
-</dependencies>
-```
-
-### Gradle
-Add it as a gradle dependency for Android Studio, in `build.gradle`:
-
-```groovy
-compile ('io.socket:socket.io-client:2.0.0') {
-  // excluding org.json which is provided by Android
-  exclude group: 'org.json', module: 'json'
-}
-```
-
-## Usage
-Socket.IO-client Java has almost the same api and features with the original JS client. You use `IO#socket` to initialize `Socket`:
-
-```java
-import io.socket.client.IO;
-import io.socket.client.Socket;
-...
-
-Socket socket = IO.socket("http://localhost");
-socket.on(Socket.EVENT_CONNECT, new Emitter.Listener() {
-
-  @Override
-  public void call(Object... args) {
-    socket.emit("foo", "hi");
-    socket.disconnect();
-  }
-
-}).on("event", new Emitter.Listener() {
-
-  @Override
-  public void call(Object... args) {}
-
-}).on(Socket.EVENT_DISCONNECT, new Emitter.Listener() {
-
-  @Override
-  public void call(Object... args) {}
-
-});
-socket.connect();
-```
-
-This Library uses [org.json](https://github.com/stleary/JSON-java) to parse and compose JSON strings:
-
-```java
-// Sending an object
-JSONObject obj = new JSONObject();
-obj.put("hello", "server");
-obj.put("binary", new byte[42]);
-socket.emit("foo", obj);
-
-// Receiving an object
-socket.on("foo", new Emitter.Listener() {
-  @Override
-  public void call(Object... args) {
-    JSONObject obj = (JSONObject)args[0];
-  }
-});
-```
-
-Options are supplied as follows:
-
-```java
-IO.Options opts = new IO.Options();
-opts.forceNew = true;
-opts.reconnection = false;
-
-socket = IO.socket("http://localhost", opts);
-```
-
-You can supply query parameters with the `query` option. NB: if you don't want to reuse a cached socket instance when the query parameter changes, you should use the `forceNew` option, the use case might be if your app allows for a user to logout, and a new user to login again:
-
-```java
-IO.Options opts = new IO.Options();
-opts.forceNew = true;
-opts.query = "auth_token=" + authToken;
-Socket socket = IO.socket("http://localhost", opts);
-```
-
-You can get a callback with `Ack` when the server received a message:
-
-```java
-socket.emit("foo", "woot", new Ack() {
-  @Override
-  public void call(Object... args) {}
-});
-```
-
-And vice versa:
-
-```java
-// ack from client to server
-socket.on("foo", new Emitter.Listener() {
-  @Override
-  public void call(Object... args) {
-    Ack ack = (Ack) args[args.length - 1];
-    ack.call();
-  }
-});
-```
-
-SSL (HTTPS, WSS) settings:
-
-```java
-OkHttpClient okHttpClient = new OkHttpClient.Builder()
-  .hostnameVerifier(myHostnameVerifier)
-  .sslSocketFactory(mySSLContext.getSocketFactory(), myX509TrustManager)
-  .build();
-
-// default settings for all sockets
-IO.setDefaultOkHttpWebSocketFactory(okHttpClient);
-IO.setDefaultOkHttpCallFactory(okHttpClient);
-
-// set as an option
-opts = new IO.Options();
-opts.callFactory = okHttpClient;
-opts.webSocketFactory = okHttpClient;
-socket = IO.socket("https://localhost", opts);
-```
-
-See the Javadoc for more details.
-
-http://socketio.github.io/socket.io-client-java/apidocs/
-
-### Transports and HTTP Headers
-You can access transports and their HTTP headers as follows.
-
-```java
-// Called upon transport creation.
-socket.io().on(Manager.EVENT_TRANSPORT, new Emitter.Listener() {
-  @Override
-  public void call(Object... args) {
-    Transport transport = (Transport)args[0];
-
-    transport.on(Transport.EVENT_REQUEST_HEADERS, new Emitter.Listener() {
-      @Override
-      public void call(Object... args) {
-        @SuppressWarnings("unchecked")
-        Map<String, List<String>> headers = (Map<String, List<String>>)args[0];
-        // modify request headers
-        headers.put("Cookie", Arrays.asList("foo=1;"));
-      }
-    });
-
-    transport.on(Transport.EVENT_RESPONSE_HEADERS, new Emitter.Listener() {
-      @Override
-      public void call(Object... args) {
-        @SuppressWarnings("unchecked")
-        Map<String, List<String>> headers = (Map<String, List<String>>)args[0];
-        // access response headers
-        String cookie = headers.get("Set-Cookie").get(0);
-      }
-    });
-  }
-});
-```
-
-## Features
-This library supports all of the features the JS client does, including events, options and upgrading transport. Android is fully supported.
+The source of this documentation is in the `src/site/` directory of the repository. Pull requests are welcome!
 
 ## License