feat: add Modbus support

lib/eModbus/README.md

@@ -0,0 +1,26 @@
+
+<img src=https://github.com/eModbus/eModbus/blob/master/eModbusLogo.png width="33%" alt="eModbus">
+
+**Read the docs at http://emodbus.github.io!**
+
+![eModbus](https://github.com/eModbus/eModbus/workflows/Building/badge.svg)
+
+This is a library to provide Modbus client (formerly known as master), server (formerly slave) and bridge/gateway functionalities for Modbus RTU, ASCII and TCP protocols.
+
+For Modbus protocol specifications, please refer to the [Modbus.org site](https://www.modbus.org/specs.php)!
+
+Modbus communication is done in separate tasks, so Modbus requests and responses are non-blocking. Callbacks are provided to prepare or receive the responses asynchronously.
+
+Key features:
+- for use in the Arduino framework
+- designed for ESP32, various interfaces supported; async versions run also on ESP8266
+- non blocking / asynchronous API
+- server, client and bridge modes
+- TCP (Ethernet, WiFi and Async), ASCII and RTU interfaces
+- all common and user-defined Modbus standard function codes 
+
+This has been developed by enthusiasts. While we do our utmost best to make robust software, do not expect any bullet-proof, industry deployable, guaranteed software. [**See the license**](https://github.com/eModbus/eModbus/blob/master/license.md) to learn about liabilities etc.
+
+We do welcome any ideas, suggestions, bug reports or questions. Please use the "[Issues](https://github.com/eModbus/eModbus/issues)" tab to report bugs and request new features and visit the "[Discussions](https://github.com/eModbus/eModbus/discussions)" tab for all else.
+
+Have fun!