docs: mention nginx config for real ip

Author: davidlougheed

readme.md

@@ -341,6 +341,11 @@ In development, you'd run:
 In production, you may need to set up these to handle persistence & HTTPS:
  - Set up an NGINX or Apache proxy with a LetsEncrypt certificate
    (see [./nginx.conf](./nginx.conf) for an example.)
+    - For the reference deployment, we are using a VM behind a proxy. We needed to set
+      the following NGINX configuration values: `real_ip_header X-Forwarded-For;` and 
+      `set_real_ip_from ####;`, where `####` is the IP block for the hypervisor from the 
+      VM's perspective, in order to get correct `X-Real-IP` values for the terms of use 
+      agreement.
  - Set up Redis to handle caching
  - Set up Postgres to handle persistent data
     - In production, make sure to configure Postgres with **lots of RAM** and 4+ workers for gathers!