Add documentation (#110)

docs/administration/nginx-reverse-proxy.md

@@ -0,0 +1,22 @@
+# Use Nginx as a reverse proxy
+
+Configure Nginx to proxy requests to Opengist. Here is an example configuration file :
+```
+server {
+    listen 80;
+    server_name opengist.example.com;
+
+    location / {
+        proxy_pass http://127.0.0.1:6157;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+    }
+}
+```
+
+Then run :
+```shell
+service nginx restart
+```