document TRANSBEAM_REVERSE_PROXY

README.md

@@ -30,6 +30,12 @@ transbeam is configured with the following environment variables:
   (default: `./static`)
 - `TRANSBEAM_PORT`: port to listen on localhost for http requests
   (default: 8080)
+- `TRANSBEAM_REVERSE_PROXY`: whether transbeam is running behind a
+  reverse proxy (recommended), or directly exposed to the internet. If
+  true, transbeam will only bind to localhost, and will use the
+  `Forwarded` or `X-Forwarded-For` headers to determine client IP
+  addresses for logs. If false, transbeam will bind on all interfaces,
+  and will always log the peer IP address. (default: true)
 - `TRANSBEAM_MAX_LIFETIME`: maximum number of days files can be kept
   for (default: 30)
 - `TRANSBEAM_MAX_UPLOAD_SIZE`: maximum size of a fileset being