docs: add nginx info

ref #18

README.md

@@ -31,3 +31,7 @@ If you are using this, it's almost certain search engines will stop indexing you
 3. Adjust the config to your needs. Options are documented with comments in the example config.
 4. Set up your IP rules if you want. These allow you to set up IPs that are automatically blocked, or allowed to access without a challenge. This is useful for e.g. search engine scrapers. Some IP ranges can be found in `example/index_bots.jsonc`.
 5. Run checkpoint with your config: `./build/checkpoint -c config.jsonc`. How you run it long-term as a service is up to you.
+
+## FAQ / Setup info
+
+See [docs/FAQ](./docs/FAQ.md).

docs/FAQ.md

@@ -0,0 +1,6 @@
+## FAQ / Setup info
+
+### Nginx / proxy
+
+In order for checkpoint to understand nginx / another reverse proxy you run on your server, make sure
+it passes the `Host` header properly to checkpoint.