DSPSpy: Create README.md

Source/DSPSpy/README.md

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+# DSPSpy
+
+DSPSpy is a homebrew tool for experimenting with the GameCube/Wii DSP.  It can also be used to dump the DSP ROMs.
+
+## Building
+
+DSPSpy is built using [devkitPPC](https://wiibrew.org/wiki/DevkitPPC); see the [devkitPro getting started page](https://devkitpro.org/wiki/Getting_Started) for more information.  DSPSpy also requires DSPTool to be built.
+
+First, run DSPTool to generate `dsp_code.h`, for instance from `tests/dsp_test.ds`.  The following commands assume an x64 Windows setup running in the DSPSpy directory:
+
+```
+../../Binary/x64/DSPTool.exe -h dsp_code tests/dsp_test.ds
+```
+
+To use the ROM-dumping code, run this:
+
+```
+../../Binary/x64/DSPTool.exe -h dsp_code util/dump_roms.ds
+```
+
+DSPTool can also generate a header for multiple DSP programs at the same time.  First, create a file (in this example, it was named `file_list.txt`) with the following contents:
+
+```
+tests/dsp_test.ds
+tests/mul_test.ds
+tests/neg_test.ds
+```
+
+Then run:
+
+```
+../../Binary/x64/DSPTool.exe -h dsp_code -m file_list.txt
+```
+
+After `dsp_code.h` has been generated, simply run `make` to generate `dspspy_wii.dol`, which can be loaded by normal means.
+
+## Dumping DSP ROMs
+
+Build DSPSpy with `util/dump_roms.ds`.  When launched, DSPSpy will automatically create files `dsp_rom.bin` and `dsp_coef.bin` on the SD card (only SD cards are supported); DSPSpy can be exited immediately afterwards.