update pid/vid config format

Author: icewind1991

cargo-espflash/README.md

@@ -90,8 +90,8 @@ An example configuration file may look as follows (note that TOML does _not_ sup
 serial = "/dev/ttyUSB0"
 
 [usb_device]
-vid = 12346 # 0x303A
-pid = 32768 # 0x8000
+vid = "303A"
+pid = "8000"
 ```
 
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