[DOCS] Theengs Plug highlight and SEO improvements (#1730)

* [DOCS] Theengs Plug highlight

* Add alt content for images and description

docs/setitup/ble.md

@@ -4,7 +4,7 @@
 
 You can use a barebone ESP32 or some nice looking products like the ones below (from M5Stack):
 
-![](../img/OpenMQTTgateway_M5_Atom_Board.png)
-![](../img/OpenMQTTgateway_M5_Stack_Board_Display_Text.png)
+![M5 Atom](../img/OpenMQTTgateway_M5_Atom_Board.png)
+![M5 Stack Core](../img/OpenMQTTgateway_M5_Stack_Board_Display_Text.png)
 
 For Arduino and ESP8266, we previously used HM10, this module is no longer supported by OpenMQTTGateway, prefer an ESP32.