doc(nginx): update readme

scripts/nginx/README.md

@@ -2,4 +2,22 @@
 
 Check the `restream.conf` file for a good-enough caching reverse proxy setup
 with nginx. It should just work with the default nginx that ships with most
-distros.
+distros. It can be copied straight to `/etc/nginx/nginx.conf` and it _should_
+just work.
+
+If you want to merge it with an existing nginx config, you can copy these
+directives to the `http` block:
+
+- `resolver` and `resolver_timeout` (if you plan on using a domain name for the
+  upstream)
+- `proxy_cache_path`
+- `upstream`
+
+And then you can copy the `server` block in too. If you want to merge it with an
+existing `server`, you can just copy all the `proxy_` directives. Note that
+it'll add caching to the whole `server` by default, so if you don't want that,
+you can change `proxy_cache` to `off`, and then in the `location` blocks where
+you do the reverse proxy, set `proxy_cache` back to `restream_cache`.
+
+Feel free to tweak the parameters to fit your needs, but generally the values in
+`restream.conf` should just work alright for caching live streams.