[Redbean] Add UuidV4 method (#1140)

tool/net/help.txt

@@ -1062,6 +1062,9 @@ FUNCTIONS
           Server Name Indicator (SNI) when performing Fetch() requests.
           This function is not available in unsecure mode.
 
+  UuidV4() -> str
+          Returns an uuid v4 string.
+
   Fetch(url:str[,body:str|{method=value:str,body=value:str,headers=table,...}])
       ├─→ status:int, {header:str=value:str,...}, body:str
       └─→ nil, error:str