flesh out the readme

README.md

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 # agbemu
 
-A mostly complete and somewhat accurate Game Boy Advance Emulator. Supports almost all of the graphics and audio subsystems. Passes many test roms including ARMWrestler, JSMolka's gba-tests, and a sizable portion of the mGBA test suite including all of the memory tests and almost all timing tests that do not require the prefetcher. It runs all games I have tested without any issue.
+A complete and somewhat accurate Game Boy Advance Emulator. Supports all of the graphics and audio subsystems, passes many test roms including ARMWrestler, JSMolka's gba-tests, and a sizable portion of the mGBA test suite including all of the memory and DMA tests and almost all timing tests that do not require the prefetcher. It runs all games I have tested without any issue.
+
+## Building
+
+This project requires SDL2 as a dependency to build and run. 
+To build first `mkdir build` and then use `make` or `make debug` to build
+a debug version or `make release` for the optimized release version.
+I have tested on both Ubuntu and MacOS.
+
+## Usage
+
+You need a GBA bios binary to run the emulator. You can dump an official one or use an open source replacement. Name the file `bios.bin` and keep it in the same directory as the executable.
+
+To run a game just run the executable with the path to the ROM as the only command line argument, or use no arguments to see other command line options.
+
+The keyboard controls are as follows:
+
+| GBA | Key |
+| --- | --- |
+| `A` | `Z` |
+| `B` | `X` |
+| `L` | `A` |
+| `R` | `S` |
+| `Dpad` | `Arrow keys` |
+| `Start` | `Return` |
+| `Select` | `RShift` |
+
+You can also connect a controller prior to starting the emulator.
+
+Hotkeys are as follows:
+
+| Control | Key |
+| ------- | --- |
+| Pause/Unpause | `P` |
+| Mute/Unmute | `M` |
+| Reset | `R` |
+| Toggle color filter | `F` |
+| Toggle speedup | `Tab` |
+
+## Credits
+
+- [GBATEK](https://www.problemkaputt.de/gbatek.htm)
+- [Tonc](https://www.coranac.com/tonc/text/toc.htm)
+- [mGBA](https://github.com/mgba-emu/mgba)
+- [EmuDev Discord Server](https://discord.gg/NUB95UKh)