Add fix for no image on recipe page

https://github.com/vabene1111/recipes/issues/470#issuecomment-787210414

docs/install/manual.md

@@ -119,6 +119,7 @@ server {
     }
 
     location / {
+        proxy_set_header Host $http_host;
         proxy_pass http://unix:/var/www/recipes/recipes.sock;
     }
 }