Added README and LICENSE.

LICENSE

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+Copyright 2022 imi415
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

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+# STM32H750VB_MRB
+
+This is a WIP reference implementation for mruby on some random STM32 boards.  
+It loads a script (`boot.rb`) from SD card, compiles to IREP and executes it.  
+
+*They do have Python*
+
+### What's working
+* mRuby core and compiler
+* UART(stdout)
+* RTOS delay
+* SD Card (FatFS)
+
+### What's not working
+* Everything else
+
+### How to build
+```bash
+mkdir build && cd build
+cmake -DCMAKE_TOOLCHAIN_FILE=arm-none-eabi.cmake  ..
+```
+
+### About targets
+`_FLASH.elf` is not working, since H750VB only got 128kB Flash
+`_RAM.elf` is mean to be loaded by a debugger, e.g. ST-LINK
+
+### Notes
+This code is highly coupled with STM32H750(caused by fixed memory map).
+A custom board design is planned.
+
+### License
+Anything comes with its own license, either in the header of the file, or listed seperately.
+Others are subject to the `LICENSE` file.
+
+### TODO
+* QUADSPI XIP bootloader
+* Driver wrappers
+* File access and `load`/`require` support
+* A custom board (hopefully)
+* Platform independent (without CubeMX)