bring back snippets docs for global header and footer app snippets

Author: alexphelps

_snippets/_view-google-tag-manager.mdx

@@ -0,0 +1,4 @@
+:::tip
+To see a full example of the features available with App Snippets, Assets, and Settings, take a look at the Google Tag Manager app on Github.
+[View Google Tag Manager App on Github](https://github.com/29next/google-tag-manager)
+:::

docs/apps/index.md

@@ -25,7 +25,7 @@ We have full featured open source example apps that provide full code examples f
 | Example Apps | Description | Link |
 | ------ | ------ | ----- |
 | Example S2S App | Server to Server demonstration of [OAuth Flow](/apps/oauth/index.md), [Session Tokens](/apps/oauth/session-auth.md), [Remote Settings](/apps/settings.md), [Webhook Setup](/webhooks.md) and [Verification](/webhooks.md#verifying-webhook-requests) | [View](https://github.com/29next/example-app) |
-| Google Analytics 4 | Demonstrates [Event Tracking](/docs/apps/event-tracking.md) to add javascript events to storefronts. | [View](https://github.com/29next/google-analytics-4) |
+| Google Analytics 4 | Demonstrates [Snippets](/docs/apps/snippets.md) and [Event Tracking](/docs/apps/event-tracking.md) to add javascript events to storefronts. | [View](https://github.com/29next/google-analytics-4) |
 | Fulfillment Service App | Demonstrates demonstration of [OAuth Flow](/apps/oauth/index.md) and the [Fulfillment Flow](/docs/apps/guides/fulfillment-service/#fulfillment-flow-overview) using the [Fulfillment APIs](/docs/api/admin/reference/#tag/fulfillment). | [View](https://github.com/29next/demo-fulfillment-service-app) |
 
 

docs/apps/snippets.md

@@ -0,0 +1,44 @@
+---
+sidebar_label: Snippets
+sidebar_position: 5
+---
+# App Snippets
+
+App Snippets are HTML template files used to extend Storefront Themes.
+
+Snippets follow the same syntax and features of [theme templates](/docs/storefront/themes/templates/index.md) which bring a full suite of tools and context available to app developers to leverage when adding custom features to a storefront.
+
+```mdx-code-block
+
+import GoogleTagManager from '@site/_snippets/_view-google-tag-manager.mdx';
+
+<GoogleTagManager />
+
+```
+
+### Locations
+
+Theme's on the 29 Next platform support `app_hooks` which are locations within storefront themes your app can target to include your snippets without needing the customize the theme itself.
+
+:::info
+To upload your snippets and manifest.json, install [App Kit](/docs/apps/app-kit.md) to zip your snippet files and push them to 29 Next.
+:::
+
+```mdx-code-block
+
+import AppHookLocations from '@site/_snippets/_app-hook-locations.mdx';
+
+<AppHookLocations />
+
+```
+
+
+### Snippet Usage Example
+
+```mdx-code-block
+
+import AppUsageExample from '@site/_snippets/_app-usage-example.mdx';
+
+<AppUsageExample />
+
+```