Add Run A Hardware Check as a mac til

mac/run-a-hardware-check.md

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+# Run A Hardware Check
+
+If your Mac is behaving in an odd way, there may be an issue with some piece
+of the hardware -- such as the RAM.
+
+You can perform a hardware check in order to chase down a diagnosis.
+
+- Shutdown your machine
+- Boot your machine
+- While it is booting, hold down the `d` key
+
+At this point, the machine should have booted into a special hardware check
+mode. Select your preferred language, the hardware check will be performed,
+and any issues will be reported.
+
+h/t Dillon Hafer