Rename README to README.md

README.md

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+# Why are there two microcontrollers?
+
+Cost and ease of development. 
+
+Both ESP8266 and ATTINY(2/4/8)5 modules can be had for around \$1 each, and
+there are retail programming jigs available. I have a kid now and don't want to
+spend my time making a programming board.
+
+The ESP8266 alone cannot really wake from multiple sources and know trap the
+source of the interrupt- there is only one pin that can wake up the micro from
+deep sleep, and that same pin needs to be used if you want to use the RTC as a
+wake source. Sure, you could use an OR-gate and also wire each source to a GPIO,
+but you might miss the source by the time the ESP wakes up to check the pins.
+
+Hence, the ATTINY is used to capture the wakeup and inform the ESP8266, who does
+the heavy lifting.
+
+## What about ESP32?
+
+The cheapest modules I can find at the time of writing are around \$3.50 apiece,
+and they can be power hungry (spikes up to 750mA compared to 400mA, from what I
+read).
+
+## What about ESP32-S2?
+
+They appear promising and are only \$2 per module on Digikey at the time of
+writing, however they are not supported by platformio yet.
+
+## What about ...?
+
+I probably wasn't aware that it exists.