Add theory to README

README.md

@@ -2,11 +2,36 @@
 
 Controls the welcome room Vestaboard directly, bypassing their cloud.
 
+![a split flap display with the words "PROTOFLAP BY PROTOSPACE"](media/signpic.jpg)
 
+## Theory
 
+Polls URL (https://api.my.protospace.ca/stats/) continuously and looks for
+changes to the `vestaboard` key. When updated, it replaces any special
+characters and then displays the message on the sign via serial.
+
+If you want to use this, just call `send_sign(text)` in protoflap.py directly.
+
+The split flap controller is connected to serial at `/dev/ttyAMA0`, 38400 baud.
+
+### See Also
+
+@Benno1308's reverse engineering:
+
+https://github.com/EngineOwningSoftware/Vestaboard-Reverse-Engineering
+
+https://www.reddit.com/r/Vestaboard/comments/tjm93n/local_device_api/
 
 ## Setup
 
+Download the Vestaboard root private key. It should be the same for all
+Vestaboards:
+
+```
+$ curl https://files.catbox.moe/kvibj6 > ~/.ssh/vestaboard
+$ chmod 600 ~/.ssh/vestaboard
+```
+
 SSH into the Vestaboard using the root key, ie:
 
 ```