Website: move demo build dir out of public/

The build-emscripten directory should not be served by local development
web servers. Ensure there is no accidental dependency by moving the
build directory outside the public folder.

The CI scripts already have the build directory outside the public
folder.

Author: strager

website/.gitignore

@@ -1 +1,2 @@
+/build-emscripten/
 /node_modules/

website/public/demo/.gitignore

@@ -1,2 +1 @@
-/build-emscripten/
 /dist/

website/public/demo/README.md

@@ -3,10 +3,10 @@
 To build the demo, install the [emscripten SDK][emscripten-sdk] and
 [Ninja][], then run the following commands:
 
-    $ cd website/public/demo  # Navigate to this directory.
-    $ emcmake cmake -S ../../.. -B build-emscripten -G Ninja -DCMAKE_BUILD_TYPE=Release
+    $ cd website
+    $ emcmake cmake -S .. -B build-emscripten -G Ninja -DCMAKE_BUILD_TYPE=Release
     $ emmake ninja -C build-emscripten quick-lint-js-wasm-demo quick-lint-js-wasm-demo-licenses
-    $ emmake cmake --install build-emscripten --component wasm-demo --prefix .
+    $ emmake cmake --install build-emscripten --component wasm-demo --prefix public/demo
 
 To run the demo on your own machine, execute the build instructions above, then
 run a static file server in the `website` directory: