docs: fix nginx configuration (#5194)

Update nginx nginx configuration in `Hosted in a subdirectory type.`

Docker/README.md

@@ -488,7 +488,7 @@ server {
 	}
 
 	location /freshrss/ {
-		proxy_pass http://freshrss;
+		proxy_pass http://freshrss/;
 		add_header X-Frame-Options SAMEORIGIN;
 		add_header X-XSS-Protection "1; mode=block";
 		proxy_redirect off;