cli: improve query tx usage text

Note explicitly that transaction hash should be specified, so instead of
an old help text:
```
$ ./bin/neo-go query tx --help
NAME:
   neo-go query tx - Query transaction status

USAGE:
   neo-go query tx [command options] [arguments...]

OPTIONS:
   --verbose, -v                   Output full tx info and execution logs
   --rpc-endpoint value, -r value  RPC node address
   --timeout value, -s value       Timeout for the operation (10 seconds by default) (default: 0s)
```
now we got the more informative one:
```
$ ./bin/neo-go query tx --help
NAME:
   neo-go query tx - Query transaction status

USAGE:
   neo-go query tx <hash> -r endpoint [-v]

OPTIONS:
   --verbose, -v                   Output full tx info and execution logs
   --rpc-endpoint value, -r value  RPC node address
   --timeout value, -s value       Timeout for the operation (10 seconds by default) (default: 0s)
```

cli/query/query.go

@@ -58,6 +58,7 @@ func NewCommands() []cli.Command {
 			{
 				Name:      "tx",
 				Usage:     "Query transaction status",
+				UsageText: "neo-go query tx <hash> -r endpoint [-v]",
 				Action:    queryTx,
 				Flags:     queryTxFlags,
 			},