docs: updated user guide\advanced

[coopmarshall]

Updated user guide with steps to secure Dispatcharr behind Nginx Proxy Manager

[MotWakorb]

A few things need changes:

1. You should include a minimum version of Nginx Proxy Manager and probably call it out as "Nginx Proxy Manager" each time, not as NPM, because NPM can also mean "node package manager" and node is used in Dispatcharr.

2. Entries like the following will trip up NPM, because checking the box for "Websockets support" creates these already:
   proxy_http_version 1.1; proxy_set_header Upgrade $http_upgrade; proxy_set_header Connection "Upgrade";

3. You should include screenshots since this is a GUI tool. Make it abundantly clear what steps are being taken.

4. I'd include TLS setup as well - I'd argue they should be able to know how to use ACME with their provider of choice, but you can also include TLS setup during the documentation, I'd add that.