[Feature request] Include in the installation instructions that ports 8181 and 5683 need to be opened
**Is your feature request related to a problem? Please describe.**
Without opening port 5683 on the server where HomeBridge is running, the shelly devices cannot connect into the homebridge-shelly plugin.  While this might be obvious to some (should have been obvious to me) it is an easy step to overlook (I overlooked it).  Include whether the /tcp or /udp or both ports need to be opened in the firewall as well.  Since different OS's open ports in different ways, you don't need to include instructions on how to open the ports to every OS, just include that they need to be opened.  E.g. "Be sure to open port 5683/udp and 8181/tcp when you install the homebridge-shelly plugin."

**Describe the solution you'd like**
I did not originally open port 5683 when I installed the homebridge-shelly plugin.  Because of this I wasted a lot of time trying to figure out why my Shelly Button 1 would not connect to homebridge even though I was seeing it communicating in the tcpdump output.  Once I realized I had not opened the port, I opened it and everything worked perfectly.  It was a simple oversight on my part but a reminder in the instructions would have saved me a lot of time.  There are others in the "issues" section who seem to also be running into closed ports and this could solve some issues before they get posted, saving everyone some time.

Thanks!