Docs: rproxy runs behind any TLS-terminating reverse proxy (closes #388)

README, SPEC and docs no longer present traefik as the required front
proxy. The README gains "The reverse proxy in front", listing what that
proxy must do: forward plain HTTP to port 8080, keep Host, set
X-Forwarded-For and X-Forwarded-Proto, and connect from an address in
SWW_RPROXY_TRUSTED_PROXIES. traefik, Caddy and nginx appear as examples,
with the nginx headers spelled out since it sets none by default.

Model: opus-5-5

docs/settings.md

@@ -478,9 +478,9 @@ start, and an invalid value stops the start. Any can be given as a file, as a
   `10.0.0.0/8,172.16.0.0/12,192.168.0.0/16`): the netblocks whose
   `X-Forwarded-For` is believed. Set but empty, it trusts nothing. A client
   outside these netblocks cannot claim another address. Where other containers
-  reach `rproxy` directly, or visitors on a private network reach traefik, they
-  can name another address in the header. Narrowing the setting to traefik's own
-  network closes that gap.
+  reach `rproxy` directly, or visitors on a private network reach the reverse
+  proxy in front, they can name another address in the header. Narrowing the
+  setting to that proxy's own network closes that gap.
 
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