remove docs dir from gitignore

Author: NikolasK-source

.gitignore

@@ -1,6 +1,6 @@
 # general
 build*
-docs/
+docs/*
 
 !docs/index.md
 !docs/_config.yml

docs/_config.yml

@@ -0,0 +1 @@
+theme: jekyll-theme-cayman

docs/index.md

@@ -0,0 +1,78 @@
+# Shared Memory Modbus TCP Client
+
+This project is a simple command line based Modbus TCP client for POXIX compatible operating systems that stores the contents of its registers in shared memory.
+
+## Basic operating principle
+
+The client creates four shared memories. 
+One for each register type:
+- Discrete Output Coils (DO)
+- Discrete Input Coils (DI)
+- Discrete Output Registers (AO)
+- Discrete Input Registers (AI)
+
+All registers are initialized with 0 at the beginning.
+The Modbus master reads and writes directly the values from these shared memories.
+
+The actual functionality of the client is realized by applications that read data from or write data to the shared memory.
+
+
+## Use the Application
+The application can be started completely without command line arguments. 
+In this case the client listens for connections on all IPs on port 502 (the default modbus port).
+The application terminates if the master disconnects.
+
+The arguments ```--port``` and ```--ip``` can be used to specify port and ip to listen to.
+
+By using the command line argument ```--monitor``` all incoming and outgoing packets are printed on stdout. 
+This option should be used carefully, as it generates large amounts of output depending on the masters polling cycle and the number of used registers.
+
+The ```--reconnect``` option can be used to specify that the application is not terminated when the master disconnects, but waits for a new connection.
+
+### Use privileged ports
+Ports below 1024 cannot be used by standard users.
+Therefore, the default modbus port (502) cannot be used without further action.
+
+Here are two ways to use the port anyway:
+#### iptables (recommended)
+An entry can be added to the iptables that forwards the packets on the actual port to a higher port.
+
+The following example redirects all tcp packets on port 502 to port 5020:
+```
+iptables -A PREROUTING -t nat -p tcp --dport 502 -j REDIRECT --to-port 5020
+```
+
+#### setcap
+The command ```setcap``` can be used to allow the application to access privileged ports.
+However, this option gives the application significantly more rights than it actually needs and should therefore be avoided.
+
+This option cannot be used with flatpaks.
+
+```
+setcap 'cap_net_bind_service=+ep' /path/to/binary
+```
+
+
+
+## Build from Source
+
+The following packages are required for building the application:
+- cmake
+- clang or gcc
+
+Additionally, the following packages are required to build the modbus library:
+- autoconf 
+- automake 
+- libtool
+
+
+Use the following commands to build the application:
+```
+git clone --recursive https://github.com/NikolasK-source/modbus_tcp_client_shm.git
+cd modbus_tcp_client_shm
+mkdir build
+cmake -B build . -DCMAKE_BUILD_TYPE=Release -DCLANG_FORMAT=OFF -DCOMPILER_WARNINGS=OFF
+cmake --build build
+```
+
+The binary is located in the build directory.