Wrong 'serial' module present can cause strange errors

The ['serial'](https://pypi.org/project/serial/) package can cause some mistakes.
the correct one is 'pyserial'

error in python2:

```
python2 simplePingExample.py --device /dev/ttyUSB0 --baudrate 115200
Opening /dev/ttyUSB0 at 115200 bps
Failed to open the given serial port
('\t', AttributeError("'module' object has no attribute 'Serial'",))
```
Python3:
```
Failed to open the given serial port
module 'serial' has no attribute 'Serial'
```

Start with simplePingExample.py and reproduce the Python 2 or Python 3 serial-port failure using the command shown. Trace how the serial module is installed and imported, then verify that the correct pyserial package provides Serial and that the example no longer reports the missing-attribute error.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.