update README with win32 build info

README.md

@@ -1,8 +1,20 @@
 # books
 
-Automatic cropping tool for cropping to books
+An intelligent bulk cropping tool
 
-## Build
+## Download
+Linux and Windows are both supported.
+
+Windows binaries are available [here](https://git.sugol.org/al/books/releases).
+
+## Building from Source
+
+### Dependencies
+ - opencv4
+ - gtkmm-4.0
+ - cairomm-1.16
+ - meson
+ - GCC or clang. C++11 support required
 
 ### Linux
 
@@ -12,16 +24,44 @@ This project uses the meson build system:
 $ meson build
 $ cd build
 $ ninja
+
+```
+
+And install with
+
+```
 $ sudo ninja install
 ```
 
 ### Windows
-Since this project uses GTK4, it's a bit difficult here (there's no GTK4 installer for Win32 just yet). However, I have built using cygwin & it seems to work ok.
+There are a couple of options for building Windows binaries. Either you can
+compile natively using `msys2`, or cross-compile from Linux.
 
-TODO: Actual build instructions
+⚠ *MSVC is unsupported* ⚠
 
-## License
+#### Native
+Install `msys2` and build as you would on Linux
+
+#### Cross-compilation
+A cross-file is included for building Windows binaries on Linux
+(`win32-cross.txt`). This file may need tweaking depending on how your `mingw`
+installation is configured. Make sure to install the relevant mingw
+dependencies.
+
+Build as you would for Linux, but substitute the first step with `meson setup
+build --cross-file=win32-cross.txt`.
+
+Good luck!
 
+#### Packaging
+A script for packaging Windows builds is included under `scripts/dist-win32.sh`.
+This should work with either `msys2` or a cross-compiled build, but you may need
+to tweak the `MINGW` variable to match your mingw installation path.
+
+The script will package the compiled executable, `.dll`s and icons into a zip
+archive for distribution.
+
+## License
 Copyright © 2021 Alister Sanders (alister@sugol.org)
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of