Fix manifest location in index

Author: jesserockz

static/index.md

@@ -6,6 +6,6 @@ Add some information about your project here.
 
 You can use the button below to install the pre-built firmware directly to your device via USB from the browser.
 
-<esp-web-install-button manifest="./manifest.json"></esp-web-install-button>
+<esp-web-install-button manifest="./firmware/manifest.json"></esp-web-install-button>
 
 <script type="module" src="https://unpkg.com/esp-web-tools@9/dist/web/install-button.js?module"></script>