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

* [DOCS] Theengs Plug highlight

* Add alt content for images and description

docs/upload/advanced-configuration.md

@@ -67,7 +67,7 @@ To your environment definition.
 
 So as to create the MQTT username and password, you have to create a new user(recommended) into Home Assistant->Configuration->Users (available in admin mode) or use an existing username/pwd combination (not recommended). This user doesn't need to be an administrator.
 
-![](../img/OpenMQTTGateway-Configuration-Home-Assistant.png)
+![MQTT User](../img/OpenMQTTGateway-Configuration-Home-Assistant.png)
 
 ::: warning
 The max size of the username is 30 and 60 for the password.
@@ -77,4 +77,4 @@ OMG will use the auto discovery functionality of home assistant to create sensor
 
 The gateway device will be available into Configuration->Devices section of Home Assistant.
 
-![](../img/OpenMQTTGateway_Home_Assistant_MQTT_discovery.png)
+![MQTT Device settings](../img/OpenMQTTGateway_Home_Assistant_MQTT_discovery.png)

docs/upload/binaries.md

@@ -73,7 +73,7 @@ If you want to upload the ready-to-go binary from Linux (or any other OS where y
 https://github.com/marcelstoer/nodemcu-pyflasher/releases
 * Execute `NodeMCU-PyFlasher`
 * Set the files and parameters as below:
-![](../img/OpenMQTTgateway_NodeMCU_PyFlasher.png)
+![NodeMCU Py Flasher](../img/OpenMQTTgateway_NodeMCU_PyFlasher.png)
 * Connect your board and select the COM port 
 * Click on *FlashNodeMCU*
 The upload details appears.

docs/upload/gitpod.md

@@ -10,9 +10,9 @@ To build OpenMQTTGateway from the web and download the binary, follow these step
 3. A first build for `esp32dev-ble` will be launched automatically. To modify the environment configuration, go to the environments.ini file in the root folder and launch the command like the one shown at the bottom of the image below:
 `platformio run -e <environment name>`
 
-![](../img/OpenMQTTGateway-Build-gitpod-env.png)
+![Gitpod build success](../img/OpenMQTTGateway-Build-gitpod-env.png)
 
 4. Wait for the server to build the binary. Once you see [SUCCESS], you can go to `.pio/build/<environment name>` and download `firmware.bin` and `partitions.bin` by right-clicking on each and selecting "Download."
-![](../img/OpenMQTTGateway-Build-gitpod.png)
+![Gitpod build download](../img/OpenMQTTGateway-Build-gitpod.png)
 
 5. Finally, follow [Option 2](binaries.md) to upload the binary.