添加一些关于midi播放的项目

Midi/music-box-stm32f1-master/freertos/readme.txt

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+Each real time kernel port consists of three files that contain the core kernel
+components and are common to every port, and one or more files that are 
+specific to a particular microcontroller and or compiler.
+
++ The FreeRTOS/Source directory contains the three files that are common to 
+every port - list.c, queue.c and tasks.c.  The kernel is contained within these 
+three files.  croutine.c implements the optional co-routine functionality - which
+is normally only used on very memory limited systems.
+
++ The FreeRTOS/Source/Portable directory contains the files that are specific to 
+a particular microcontroller and or compiler.
+
++ The FreeRTOS/Source/include directory contains the real time kernel header 
+files.
+
+See the readme file in the FreeRTOS/Source/Portable directory for more 
+information.