Add Emscripten to README

README.md

@@ -31,6 +31,7 @@ Some of the major features currently implemented are:
   * Multiuser support on Windows systems (user specific game data
     is stored in "%APPDATA%\Quake3")
   * PNG support
+  * Web support via Emscripten
   * Many, many bug fixes
 
 The map editor and associated compiling tools are not included. We suggest you
@@ -98,6 +99,23 @@ For macOS, building a Universal Binary 2 (macOS 10.9+, arm64, x86_64)
   4. Copy the resulting ioquake3.app in /build/release-darwin-universal2
      to your /Applications/ioquake3 folder.
 
+For Web, building with Emscripten
+  1. Follow the installation instructions for the Emscripten SDK including
+     setting up the environment with emsdk_env.
+  2. Copy or symlink your baseq3 directory into this directory so Emscripten
+     can package your game files. (Alternatively, you can build without this,
+     and provide the game data files at runtime. For this, game files should
+     be listed in `ioq3-config.json`)
+  3. Run `emmake make debug` (or release, but if you do both then you will
+     need to pass an extra URL parameter to the HTML file to select the
+     build you want).
+  4. Start a web server serving this directory. `python3 -m http.server`
+     is an easy default that you may already have installed.
+  5. Open `code/web/ioquake3.html` in a web browser. Open the developer
+     console to see errors and warnings.
+  6. Debugging the C code is possible using a Chrome extension. For details
+     see https://developer.chrome.com/blog/wasm-debugging-2020
+
 Installation, for *nix
   1. Set the COPYDIR variable in the shell to be where you installed Quake 3
      to. By default it will be /usr/local/games/quake3 if you haven't set it.