Add information about bind to UDP port 69 without root privileges

Author: zentarim

README.md

@@ -88,4 +88,7 @@ In this example:
 - Supported TFTP options:
     - timeout 
     - blksize
-    - tsize
+    - tsize
+- The daemon is intended to run without root privileges. To allow RTFTP to bind to UDP port 69, one of following workarounds may be applied:
+    - Add **CAP_NET_BIND_SERVICE** capability to RTFTP: `setcap 'cap_net_bind_service=+ep' /path/to/rtftp`
+    - Start RTFTP via `authbind` with port 69 allowed for the RTFTP user: `touch /etc/authbind/byport/69 && chown <rtftp_user>:<rtftp_group> /etc/authbind/byport/69`