add note about FreeBSD

README.md

@@ -13,3 +13,20 @@ busybox httpd -vv -fp 8080
 ```
 
 And then open `http://localhost:8080` in your browser.
+
+### FreeBSD
+
+The demo syntax used in the interpreter script is not compatible with FreeBSD's `sh`.
+The following patch makes it use the default Busybox `ash` applet installed via `pkg install busybox`:
+
+```diff
+diff --git a/interpreter.server_core_internal b/interpreter.server_core_internal
+index 097f55f..604fe7f 100755
+--- a/interpreter.server_core_internal
++++ b/interpreter.server_core_internal
+@@ -1,4 +1,4 @@
+-#!/bin/sh
++#!/usr/local/bin/busybox ash
+
+ server_core_internal_file="${1:-index.html}"
+```