Add known issues and Modbus register for older software versions

CHANGELOG.md

@@ -7,6 +7,7 @@
 * Add `-v` option which enables debug logging
 * Start using ESLint, add `no-console` rule to enforce use of logger instances
 * Include the unit's Modbus address in the device information
+* Add a section about older software versions to the README
 
 ## 2.3.2
 

README.md

@@ -379,6 +379,9 @@ in Home Assistant automatically through the MQTT integration. The following enti
   these values to find something that suits your use case, or trust the built-in automation in the ventilation unit to 
   do its job.
 
+* Older firmware (e.g. Pingvin devices with software version 2.01) only support a smaller list of Modbus registers, so 
+  some functionality may be missing. Open an issue if you feel like something isn't working that should be working.
+
 ## Troubleshooting
 
 See [docs/CONNECTION.md](./docs/CONNECTION.md)

docs/CONNECTION.md

@@ -34,4 +34,6 @@ If you have connected everything but the software is unable to read anything fro
 manifests as various timeouts), try the following:
 
 * try reversing the A and B (sometimes called RX and TX or + and -)
-* try using slave address 0 instead of 1 (`--modbusSlave 0`)
+* verify that you're using the correct slave address by looking up the "Modbus address" from the control panel (see 
+  manual for password)
+* if your unit is set to use slave address 0, change it to 1. The address 0 has special meaning and should not be used.