temp: Add a README

Misc/Temp-Monitor/README.md

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+Millikelvin Temperature Monitor
+-------------------------------
+Because we are fighting a lot of drift issues with the STM, we assume that
+temperature deviations have a catastrophic effect on the system.  To gain some
+insights, we built a little temperature minitor for correlating the STM drift
+to temperature fluctuations.
+
+### Hardware
+The following components were used:
+
+- A cheap `MF52D 3950K` 10k NTC thermistor
+- An ADC breakout board based on the CS1237 chip ([Breakout Board Docs](https://github.com/yasir-shahzad/CS1237-24-Bit-ADC-Module))
+- A Raspberry Pi Pico 2
+
+![Schematic of the temperature monitoring setup](./schematic.png)
+
+### Software
+On the Pico 2, a small micropython script is running.  To deploy the code, you
+need [`mpremote`](https://docs.micropython.org/en/latest/reference/mpremote.html):
+
+```bash
+mpremote cp cs1237.py :
+mpremote cp temperature_monitor.py :
+mpremote cp main.py :
+```
+
+Replug the Pico USB cable and data should be sent in over serial.
+
+To monitor, we are currently using the [`serial-monitor-rust`](https://github.com/hacknus/serial-monitor-rust) tool.