Update README.md

[aminsaedi]

Added X-Forwarded-Host to the nginx reverse proxy options as it's used in the code (app/utils/misc.py - line 84)

If X-Forwarded-Host is not set and the app is running behind nginx on any ports other than 80/433, then the port number in the URL returned by get_proxy_host_url function will be ignored

I'm running the Whoogle behind nginx reverse proxy on port 2053, The images were not displayed for me because url of images was https://mydomain.com/element?... instead of https://mydomain.com:2053/element?.... After checking the code I was able to resolve it by adding proxy_set_header X-Forwarded-Host $http_host; to my nginx config file