minor: Add EcoWitt, FineOffset, Govee device notes

Author: zuckschwerdt

src/devices/ecowitt.c

@@ -14,7 +14,7 @@ Ecowitt Wireless Outdoor Thermometer WH53/WH0280/WH0281A.
 55-bit one-row data packet format (inclusive ranges, 0-indexed):
 
 |  0-6  | 7-bit header, ignored for checksum, always 1111111
-|  7-14 | Always 01010011
+|  7-14 | Model code, 0x53
 | 15-22 | Sensor ID, randomly reinitialized on boot
 | 23-24 | Always 00
 | 25-26 | 2-bit sensor channel, selectable on back of sensor {00=1, 01=2, 10=3}

src/devices/fineoffset.c

@@ -448,16 +448,17 @@ Example: 22.6 C, 40 %, 1001.7 hPa
 Data layout:
 
     aa 2d d4 e5 02 72 28 27 21 c9 bb aa
-             ?I IT TT HH PP PP CC BB
+             MI IT TT HH PP PP CC XX
 
+- M: 4 bit Model code, 0xd: old model, 0xe: new model.
 - I: 8 bit Sensor ID (based on 2 different sensors). Does not change at battery change.
 - B: 1 bit low battery indicator
 - F: 1 bit invalid reading indicator
 - T: 10 bit Temperature (+40*10), top two bits are flags
 - H: 8 bit Humidity
 - P: 16 bit Pressure (*10)
 - C: 8 bit Checksum of previous 6 bytes (binary sum truncated to 8 bit)
-- B: 8 bit Bitsum (XOR) of the 6 data bytes (high and low nibble exchanged)
+- X: 8 bit Bitsum (XOR) of the 6 data bytes (high and low nibble exchanged)
 
 WH32B is the same as WH25 but two packets in one transmission of {971} and XOR sum missing.
 

src/devices/govee.c

@@ -22,6 +22,10 @@ NOTE: The Govee Door Contact sensors only send a message when the contact
       is opened.
       Unfortunately, it does NOT send a message when the contact is closed.
 
+Data layout:
+
+    II II ?E DD ?? XX
+
 - A data packet is 6 bytes, 48 bits.
 - Bits are likely inverted (short=0, long=1)
 - First 2 bytes are the ID.
@@ -35,6 +39,10 @@ NOTE: The Govee Door Contact sensors only send a message when the contact
 - Last byte contains the parity bits in index 2-6 (101PPPP1).
   The parity checksum using CRC8 against the first 5 bytes
 
+Data decoding:
+
+    ID:8h8h ?4h EVENT:4h EVENTDATA:8h ?8h CHK:3b 4h 1b
+
 Battery levels:
 
 - 100 : 5 Bars