Add note about AppleDouble in MxBuild docs

[envialon]

On this story we add a note about possible file incompatibilities due to AppleDouble for mx11 and mx10, I've placed it on the MxBuild file after the example alarm, but feel free to move it to a more convenient spot.

This change is not tied to any particular release and it can be merged at your earliest convenience :)

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✅ quinntracy
❌ Enrique

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