Add web target to SDL example (without SDL3 files)

examples/sdl_app/.gitignore

@@ -2,3 +2,7 @@
 /build
 /build.ninja
 /shuriken.override.yaml
+
+# SDL3 files
+/lib
+/vendor

examples/sdl_app/shuriken.yaml

@@ -8,3 +8,17 @@ default_target: linux
 targets:
   linux:
     output_file: sdl_example
+
+  # NOTE: To build for web, you need a) emscripten installed on your system, b) the SDL3 and SDL3_image headers in the
+  # vendor directory, and c) static libraries for SDL3 and SDL3_image compiled for WebAssembly in the lib directory.
+  # These are not contained in this repository to keep the repository data small.
+  web:
+    cpp_compiler: em++
+    cpp_flags_extra: -Ivendor
+    linker_args: >-
+      lib/web/libSDL3.a
+      lib/web/libSDL3_image.a
+      --use-preload-plugins
+      --preload-file assets/
+    output_file: output/index.html
+    run_command: python -m http.server -d build/web/output