Update sing-box.md

content/docs/configuration/vpn-backends/sing-box.md

@@ -57,5 +57,9 @@ services:
 
 Make sure `/var/lib/marznode/sing-box.json` exists, and is a valid sing-box config.
 
+## Current Limitations
+- There is no user-management api implemented on sing-box, hence each time list of users is modified for any of the inbounds related to a sing-box backend, the list is written into sing-box configuration and a SIGHUP signal is sent to the corresponding sing-box process; notifying it to reload the configuration file.
+- Some protocols are not yet implemented for sing-box.
+
 ## See also
-- [configuration documents](https://sing-box.sagernet.org/configuration/)
+- [sing-box configuration documents](https://sing-box.sagernet.org/configuration/)