broken video link in `rel/doc/a2_build_video.md`

[kzall0c]

If it's a short video described, it's probably better to upload the video file or youtube link directly rather than using Google Drive,
also that link A2O Build Process is currently inaccessible.

This is a short video showing the build process for A2O, as described in rel/readme.md.
A2O Build Process

• https://drive.google.com/file/d/1pnQPitj_bAIfMufECAyA3CQfx0bt8UYB/view?usp=sharing