Add index.html to nix build output

Makefile

@@ -27,6 +27,7 @@ dist/app.c: dist/index.html $(OTHER_SRC)
 	echo -e "/,./release/index.html\n/test.html,./dist/index.html\n/$$(ls dist/*.bin|cut -d/ -f2),$$(ls ./dist/*.bin)\n/manifest.json,./src/manifest.json\n/logo.png,./src/logo.png\n/favicon.ico,./src/favicon.ico" | sh epic.sh > $@
 
 install: dist/app.wasm dist/app.did
+	install -D dist/index.html ${out}/share/index.html
 	install -D dist/app.did ${out}/bin/ic-qr-scanner.did
 	install -D dist/app.wasm ${out}/bin/ic-qr-scanner.wasm