Add extra port open, and add ser2net example to README

[tedvdb]

I'm using this component combined with ser2net. This allows me to have a simple device with a USB port in the utility closet, and have my HA instance running somewhere else in the network.

Since using ser2net is less reliable, and TCP connections sometimes drop, this PR repairs that connection.

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 77.90%. Comparing base (bcb42df) to head (90a3b4d).

Files	Patch %	Lines
...tom_components/kamstrup_403/pykamstrup/kamstrup.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #124      +/-   ##
==========================================
+ Coverage   77.87%   77.90%   +0.02%     
==========================================
  Files           8        8              
  Lines         357      362       +5     
==========================================
+ Hits          278      282       +4     
- Misses         79       80       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[golles]

Thank you Ted! I will test it out during the weekend.

Can you pull my latest main (commit: bcb42df) into your PR? That should fix the failing CI check.

[golles]

Thanks again Ted!