Write some docs.

README.md

@@ -1,7 +1,64 @@
-### Dependencies
+## dhc
 
-[ninja](https://ninja-build.org): `sudo apt-get install ninja-build`
+dhc is a DirectInput/XInput wrapper DLL that implements controller hotplugging
+for games that don't do so themselves. It pretends that there are always a
+configurable number of PS4 controllers plugged in at a time, and maps the
+inputs of real controllers onto them.
 
-[meson](http://mesonbuild.com): `sudo apt-get install python3-pip && pip install meson`
+### Installation
 
-[MinGW-w64](https://sourceforge.net/projects/mingw-w64/): `sudo apt-get install mingw-w64`
+Download [the latest release](https://github.com/jmgao/dhc/releases) and place
+the appropriate DLLs in the same folder as the game you want to use dhc with.
+Note that the game binary might be not be the one that's at the top level of
+the game's directory: if you don't see dhc.log or dhc.toml files being created
+after you start the game, you probably chose the wrong one. You can right click
+on the game in Task Manager and use properties to find the location of the
+actual binary.
+
+### Compiling
+
+dhc is implemented in both C++ and rust, so you'll need working toolchains for
+both languages. Only cross-compilation from Linux has been tested, so if you
+want to build on a Windows host, you'll either have fun figuring it out, or
+just use WSL or a Linux VM.
+
+Install the dependencies:
+```sh
+sudo apt-get install ninja-build
+sudo apt-get install python3-pip && pip3 install meson
+sudo apt-get install mingw-w64
+
+# Install rust
+curl https://sh.rustup.rs -sSf | sh -s -- -y
+# Restart your shell or source your profile to make sure rustup and cargo are on your $PATH
+
+# Add rust's cross compilation targets
+rustup target add i686-pc-windows-gnu x86_64-pc-windows-gnu
+
+# Install cbindgen
+cargo install cbindgen
+```
+
+And then build:
+```
+git clone https://github.com/jmgao/dhc.git
+cd dhc
+./build/generate.sh
+ninja -C build/i686 install && ninja -C build/x86_64 install
+```
+
+The built DLLs will be copied into `dist/{i686, x86_64}`.
+
+### Known issues
+
+- XInput emulation is currently implemented as a no-op that pretends that no
+  controllers are connected. This should only affect games that weren't actually
+  finished before releasing (i.e. SF5).
+
+- XInput controllers only get their triggers forwarded as digital buttons, not
+  analog values.
+
+- Steam's controller emulation will put itself on top of dhc, which will result
+  in controllers showing up multiple times. To avoid this, either launch the
+  game with no controllers connected, or disable Steam's controller support
+  (View > Settings > Controller > General Controller Settings > uncheck everything).