m: add page (#2473)

pages/osx/m.md

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+# m
+
+> Swiss Army Knife for macOS.
+
+- Get the battery status:
+
+`m battery status`
+
+- Turn off bluetooth:
+
+`m bluetooth off`
+
+- List available filesystems for formatting:
+
+`m disk filesystems`
+
+- Enable Dock's auto hide feature:
+
+`m dock autohide YES`
+
+- Disable the firewall:
+
+`m firewall disable`