Add a brief tutorial about debugging MinGW GCC build on Windows

[pzhlkj6612]

We need WinDbg and rainers/cv2pdb, and they are working for me. I'm guessing that ssbssa/gdb may also work.

Refs:

• How can I debug a MinGW EXE with the Microsoft Visual C++ debugger? - Stack Overflow https://stackoverflow.com/q/274566
• rainers/cv2pdb: converter of DMD CodeView/DWARF debug information to PDB files https://github.com/rainers/cv2pdb
• ssbssa/gdb: Unofficial Windows build of gdb with added features. https://github.com/ssbssa/gdb

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