[DOCS] Page speed optimizations (#1922)

* [DOCS] Page speed optimizations

* Fix img path

docs/prerequisites/board.md

@@ -17,7 +17,11 @@ If you want to use the BLE decoding capabilities of OpenMQTTGateway with a table
 
 [Theengs bridge](https://shop.theengs.io/products/theengs-bridge-esp32-ble-mqtt-gateway-with-ethernet-and-external-antenna) is a powerful BLE to MQTT gateway for over [90 sensors](https://decoder.theengs.io/devices/devices.html). Equipped with an Ethernet port, and external antenna, ensuring an enhanced range for your BLE sensors. It supports also WiFi connectivity.
 
-[![Theengs bridge view](../img/Theengs-Bridge-ble-gateway.png)](https://shop.theengs.io/products/theengs-bridge-esp32-ble-mqtt-gateway-with-ethernet-and-external-antenna)
+<div style="text-align: center;">
+    <a href="https://shop.theengs.io/products/theengs-bridge-esp32-ble-mqtt-gateway-with-ethernet-and-external-antenna" target="_blank" rel="noopener noreferrer">
+    <img src="/img/Theengs-Bridge-ble-gateway.png" alt="Theengs bridge view" width="375" height="501">
+    </a>
+</div>
 
 [Theengs plug](https://shop.theengs.io/products/theengs-plug-smart-plug-ble-gateway-and-energy-consumption) is available flashed with OpenMQTTGateway, and brings the functions below:
 * BLE to MQTT gateway, tens of Bluetooth devices supported thanks to Theengs Decoder library. The plug uses an ESP32 acting as a BLE to Wifi gateway to scan, decode and forward the data of the nearby sensors,
@@ -27,7 +31,11 @@ If you want to use the BLE decoding capabilities of OpenMQTTGateway with a table
 * Presence detection (beta),
 * Local connectivity first.
 
-[![Theengs plug view](../img/Theengs-Plug-OpenMQTTGateway.png)](https://shop.theengs.io/products/theengs-plug-smart-plug-ble-gateway-and-energy-consumption)
+<div style="text-align: center;">
+    <a href="https://shop.theengs.io/products/theengs-plug-smart-plug-ble-gateway-and-energy-consumption" target="_blank" rel="noopener noreferrer">
+    <img src="/img/Theengs-Plug-OpenMQTTGateway.png" alt="Theengs plug view" width="268" height="453">
+    </a>
+</div>
 
 Support the project by purchasing the [Theengs bridge](https://shop.theengs.io/products/theengs-bridge-esp32-ble-mqtt-gateway-with-ethernet-and-external-antenna) or the [Theengs plug](https://shop.theengs.io/products/theengs-plug-smart-plug-ble-gateway-and-energy-consumption)
 The plug is available in North America only, other regions are planned.