Add MQTT Viewer to list of desktop tools

[samfweb]

Could you add MQTT Viewer (http://mqttviewer.app) to the list of desktop MQTT tools?

It's new, fast and a really easy way to debug and visualise MQTT data (including Sparkplug).

[B-Weiss]

Hi Sam, sure, your contribution can be added to the list of MQTT tools. To proceed here, please add it to the list yourself and create a pull request. We will merge it.

Thanks!

[ChxGuillaume]

@samfweb feel free to check out the PR to see if you're ok with the "description" for MQTT Viewer, I took your tagline from your GitHub repo Description 👍