Add documentation for Seeed XIAO ESP32C3 Create xiao-esp32c3.md

[tianrking]

Dear TinyGo maintainers,

This PR introduces the following improvements:

1. Detailed overview of the Seeed XIAO ESP32C3 board and its capabilities.
2. Comprehensive pin mapping information, including GPIO, UART, I2C, and SPI pins.
3. Clear instructions for building and flashing TinyGo programs to the XIAO ESP32C3.
4. A practical example demonstrating UART communication on the board.

Key additions include:

• Accurate interface support information
• Detailed pin configuration table
• Step-by-step flashing instructions
• Advanced building options with explanations of various flags
• A working UART example to help users get started quickly

These additions aim to make it easier for TinyGo users to work with the XIAO ESP32C3 board, potentially broadening TinyGo's reach in the ESP32 ecosystem.

I have tested the provided information and example on the actual hardware to ensure accuracy. However, I welcome any feedback or suggestions for improvement.

Thank you for considering this contribution. I look forward to your review and am happy to make any necessary adjustments.

[tianrking]

@deadprogram @aykevl