Improve the build instructions a bit

README.md

@@ -26,17 +26,34 @@ All other dependencies are either stored in the repository or are included as su
 
 Building:
 
-1. Clone Aegisub's repository recursively to fetch it and all submodules: `git clone --recursive [email protected]:Aegisub/Aegisub.git`
+1. Clone Aegisub's repository recursively to fetch it and all submodules: `git clone --recursive [email protected]:Aegisub/Aegisub.git` This will take quite a while and requires about 2.5 GB of disk space.
 2. Open Aegisub.sln
-3. Build the solution.
-4. Copy the contents of an existing Aegisub install into the aegisub/aegisub/bin directory (not strictly required, but you'll be missing a lot of functionality otherwise).
+3. Build the BuildTasks project.
+4. Build the entire solution.
 
-For actual development work you will probably want to mostly use the
-"Debug-MinDep" configuration (which disables building most of the projects), as
-the dependency checking is pretty slow.
+You should now have a `bin` directory in your Aegisub directory which contains `aegisub32d.exe`, along with a pile of other files.
+
+The Aegisub installer includes some files not built as part of Aegisub (such as Avisynth and VSFilter), so for a fully functional copy of Aegisub you now need to copy all of the files from an installed copy of Aegisub into your `bin` directory (and don't overwrite any of the files already there).
+You'll also either need to copy the `automation` directory into the `bin` directory, or edit your automation search paths to include the `automation` directory in the source tree.
+
+After building the solution once, you'll want to switch to the Debug-MinDep configuration, which skips checking if the dependencies are out of date, as that takes a while.
+
+### OS X
+
+A vaguely recent version of Xcode and the corresponding command-line tools are required.
+Nothing older than Xcode 5 has been tested recently, but it is likely that some later versions of Xcode 4 are good enough.
+
+For personal usage, you can use homebrew to install almost all of Aegisub's dependencies:
+
+	brew install boost --c++11 --with-icu
+	brew install autoconf ffmpeg fontconfig freetype2 fftw3 fribidi libass wxmac
+
+[ffms2](http://github.com/FFMS/ffms2) currently does not have a homebrew formula, but with ffmpeg installed should be a simple `./configure && make && make install` to install.
+
+Once the dependencies are installed, build Aegisub with `autoreconf && ./configure && make && make osx-bundle`.
+`autoreconf` should be skipped if you are building from a source tarball rather than `git`.
 
 ## License
 
-All source files in this repository are licensed under either 3-clause BSD or
-ISC licenses. In practice, Aegisub binaries are usually GPL licensed due to the
-dependencies.
+All files in this repository are licensed under various GPL-compatible BSD-style licenses; see LICENCE and the individual source files for more information.
+The official Windows and OS X builds are GPLv2 due to including fftw3.