Update TLS.md

[hkspks]

Added instructions to reset the TLS fingerprint - a common issue, if the fingerprint changes due to server reconfiguration.

[s-hadinger]

I'm converned. If you zero both fingerprints, then you make your device very vulnerable. Your legit server will be recognized as first fingerprint. When a rogue server shows up, it will take the second slots, hence defeating the purpose.

You should keep the original fingerprint and zero only one of them at the same time.

[hkspks]

Thanks @s-hadinger, let's add this to the doc just to remove one fingerprint. For my interest: How are the fingerprints set at a fresh installation? I wanted to trigger a "factory reset". Furthermore a speaking error message would be great on the console, if the fingerprint of the server has changed. I got the following message and was kind of lucky to find the source of the problem:

11:50:18.211 MQT: TLS connection error: 1 11:50:18.213 MQT: Connect failed to <server-ip>:8883, rc -2. Retry in 20 sec