Update usage

Author: NikolasK-source

README.md

@@ -25,6 +25,15 @@ Modbus_TCP_client_shm [OPTION...]
   -m, --monitor           output all incoming and outgoing packets to stdout
   -r, --reconnect         do not terminate if Master disconnects.
   -h, --help              print usage
+
+
+The modbus registers are mapped to shared memory objects:
+    type | name                      | master-access   | shm name
+    -----|---------------------------|-----------------|----------------
+    DO   | Discrete Output Coils     | read-write      | <name-prefix>DO
+    DI   | Discrete Input Coils      | read-only       | <name-prefix>DI
+    AO   | Discrete Output Registers | read-write      | <name-prefix>AO
+    AI   | Discrete Input Registers  | read-only       | <name-prefix>AI
 ```
 
 ## Libraries

src/main.cpp

@@ -89,6 +89,14 @@ int main(int argc, char **argv) {
         options.set_width(120);
         std::cout << options.help() << std::endl;
         std::cout << std::endl;
+        std::cout << "The modbus registers are mapped to shared memory objects:" << std::endl;
+        std::cout << "    type | name                      | master-access   | shm name" << std::endl;
+        std::cout << "    -----|---------------------------|-----------------|----------------" << std::endl;
+        std::cout << "    DO   | Discrete Output Coils     | read-write      | <name-prefix>DO" << std::endl;
+        std::cout << "    DI   | Discrete Input Coils      | read-only       | <name-prefix>DI" << std::endl;
+        std::cout << "    AO   | Discrete Output Registers | read-write      | <name-prefix>AO" << std::endl;
+        std::cout << "    AI   | Discrete Input Registers  | read-only       | <name-prefix>AI" << std::endl;
+        std::cout << std::endl;
         std::cout << "This application uses the following libraries:" << std::endl;
         std::cout << "  - cxxopts by jarro2783 (https://github.com/jarro2783/cxxopts)" << std::endl;
         std::cout << "  - libmodbus by Stéphane Raimbault (https://github.com/stephane/libmodbus)" << std::endl;