Add some information about the CAN bus of ND Miatas

can_db/mazda_mx5_nd.md

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+# Mazda MX-5 Miata (ND generation)
+
+Here is information on some of the PIDs that you're most likely to use with
+RaceChrono and equations to get the right scale, etc.
+
+These PIDs were tested on 2019 Mazda MX-5 Miata RF, but should apply to other
+model years of the ND generation as well. If you find any mistakes, or model
+year specific PIDs, please send a pull request!
+
+## Recommended PIDs:
+
+Here are PIDs and RaceChrono equations for data channels that should be enough
+for most people:
+
+Channel name | PID | Equation | Notes
+------------ | --- | -------- | -----
+Accelerator position (%) | 514 | `E/2.5` |
+Brake position (%) | 120 | `max(0, 100 + bytesToInt(raw, 4, 1)) / 2.55` | Might need more work, possibly a different scale
+Steering angle | 134 | `(16000 - bytesToUInt(raw, 0, 2)) * 0.1` | Positive value = turning right. You can add a `-` if you prefer it the other way around.
+Speed | 514 | `bytesToInt(raw, 2, 2) / 360.0` |
+Engine RPM | 514 | `bytesToUInt(raw, 0, 2) / 4` | If someone records >8192 rpms to confirm, let me know :)
+
+### Would be nice to find PIDs for ...
+
+Essentials: fuel level, coolant temperature, clutch pedal, current gear.
+
+Advanced: tire pressures, tire temperatures, lat/long acceleration (if
+available), yaw rate, individual wheel speeds.