Add WiFi Multi to readme.rst

doc/esp8266wifi/readme.rst

@@ -156,6 +156,39 @@ The Client class creates `clients <https://en.wikipedia.org/wiki/Client_(computi
 
 Check out the separate section with `list of functions <client-class.rst>`__
 
+WiFi Multi
+~~~~~~~~~~
+
+`ESP8266WiFiMulti.h` can be used to connect to a WiFi network with strongest WiFi signal (RSSI). This requires registering one or more access points with SSID and password. It automatically switches to another WiFi network when the WiFi connection is lost.
+
+Example:
+
+.. code:: cpp
+    #include <ESP8266WiFiMulti.h>
+
+    ESP8266WiFiMulti wifiMulti;
+
+    // WiFi connect timeout per AP. Increase when connecting takes longer.
+    const uint32_t connectTimeoutMs = 5000;
+
+    void setup()
+    {
+      // Set in station mode
+      WiFi.mode(WIFI_STA);
+
+      // Register multi WiFi networks
+      wifiMulti.addAP("ssid_from_AP_1", "your_password_for_AP_1");
+      wifiMulti.addAP("ssid_from_AP_2", "your_password_for_AP_2");
+      wifiMulti.addAP("ssid_from_AP_3", "your_password_for_AP_3");
+    }
+
+    void loop()
+    {
+      // Maintain WiFi connection
+      if (wifiMulti.run(connectTimeoutMs) == WL_CONNECTED) {
+          ...
+      }
+    }
 
 BearSSL Client Secure and Server Secure
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~