add mqtt demo

board/Linux_Posix/mqtt_demo/readme.md

@@ -0,0 +1,47 @@
+# How to run the demo in linux
+
+## step1
+make sure your develop environment.
++ `cmake` and version greater than 3.8.2
++ `gcc` `gdb` `make` is installed
+
+## step2
+generate `mqtt_config.h` file to replace `./inc/mqtt_config.h`
+
+cd `tiny/tools/` directory, run python script
+```bash
+python3 mqtt_config_gen.py
+```
+
+then input your server configuration, generate `mqtt_config.h` file
+copy to `./inc/` replace old file
+
+## step3
+make `build` directory and compile in `build`
+
+```bash
+mkdir build && cd build
+cmake ..
+make
+```
+
+## step4
+run program !!
+
+```bash
+# in build directory
+./mqtt_demo
+```
+
+## other
+you can copy this demo to other path, but if you want do it,
+you need modify `CMakeLists.txt`. find line
+
+```cmake
+set(TINY_ROOT ../../../)
+```
+
+and modify `path-to-tinyos`
+```cmake
+set(TINY_ROOT path-to-tinyos)
+```