Update hysteria2.en.md

Author: wwqgtxx

docs/config/proxies/hysteria2.en.md

@@ -40,6 +40,8 @@ Authentication password.
 
 Port hop interval, in seconds, default is 30.
 
+Entering "15-30" will randomly select one of the values ​​as the switching interval each time. Only a range is supported (commas are not allowed).
+
 ## up/down
 
 Brutal rate control; if no unit is specified, the default is Mbps.