instruction for solving issue with this error : " AttributeError: module 'em' has no attribute 'BUFFERED_OPT' when building firmware for esp32 on udp transfering

## Issue template

- Hardware description: esp32
- RTOS: freeRtos
- Installation type: micro_ros_setup
- Version or commit hash: version of micro-ROS used: galactic for Ubuntu 20.04

#### Steps to reproduce the issue
Assuming you have already setup the firmware using `ros2 run micro_ros_setup create_firmware_ws.sh freertos esp32` and after proper wifi configuration, when you try to build the firmware for udp transferring using `ros2 run micro_ros_setup build_firmware.sh` you will most likely get an error which related to the Python environment and the em (Empy) module. The specific error is:
```
AttributeError: module 'em' has no attribute 'BUFFERED_OPT'
```

#### To resolve this issue, follow these steps:

1. First, deactivate any active Python virtual environments:

```
deactivate
```

To install empy in the specific Python environment used by the build process, you should use the pip associated with that Python installation. Here's the command to install empy version 3.3.4 in that environment:
```
~/microros_ws/firmware/toolchain/espressif/python_env/idf4.1_py3.8_env/bin/pip3 install empy==3.3.4
```
2. After that, verify the installation:
```
~/microros_ws/firmware/toolchain/espressif/python_env/idf4.1_py3.8_env/bin/python3 -c "import em; print(em.__file__)"
```

3. Update setuptools and wheel:
```
~/microros_ws/firmware/toolchain/espressif/python_env/idf4.1_py3.8_env/bin/pip3 install --upgrade setuptools wheel
```

5. Clean your micro-ROS workspace:

```bash
cd ~/microros_ws
rm -rf build install log
```

6. Rebuild the workspace:

```bash
colcon build --symlink-install
```

7. Source the setup file:

```bash
source install/local_setup.bash
```

8. Try building the firmware again:

```bash
ros2 run micro_ros_setup build_firmware.sh
```

Start with the reported `ros2 run micro_ros_setup build_firmware.sh` failure and the ESP32 Python environment at `firmware/toolchain/espressif/python_env/idf4.1_py3.8_env`. Verify the `em.BUFFERED_OPT` error and the listed Empy installation steps, then determine where this workaround should be documented; done means the firmware build instructions clearly cover the error and recovery.

Written by the indexing model from the issue text.