chore: add usage docs for seo

docs/seo.md

@@ -0,0 +1,57 @@
+# SEO Metadata
+
+SnapWP exports two main functions to add meta tags for SEO:
+
+-   `getLayoutMetadata`: Gets SEO data for the site.
+-   `getPageMetadata`: Gets SEO data related to the template. Adds update icon
+
+## Registering a new plugin
+
+The SEO functionality can be extended by registering new plugins. Below is an example of updated root layout.
+
+```typescript
+import { RootLayout } from '@snapwp/next';
+import { getLayoutMetadata, Seo } from '@snapwp/next/seo';
+import type { Metadata } from 'next';
+import type { PropsWithChildren } from 'react';
+
+// Register a plugin before calling function `getLayoutMetadata`
+Seo.registerPlugin(
+	{
+		fragment: PluginFragmentDoc,
+		parseMetadata: parserFunction,
+		location:'page'
+	}
+);
+
+export default function Layout( { children }: PropsWithChildren ) {
+	return (
+		<RootLayout>
+			<>{ children }</>
+		</RootLayout>
+	);
+}
+
+/**
+ * Generate site meta data.
+ * @return Metadata for SEO.
+ */
+export async function generateMetadata(): Promise< Metadata > {
+	const metadata = await getLayoutMetadata();
+
+	return {
+		...metadata,
+	};
+}
+```
+
+## Anatomy of a SEO plugin
+
+An plugin requires 3 things to be registered.
+
+-   **Fragment** to define the data needed from the WP server.
+-   **Parser** to parse the fragment data to be consumable by NextJS.
+-   **Location** has value of either `page` or `layout`. This defines if the parsed meta data should be added to the returned value of `getPageMetadata` or `getLayoutMetadata`.
+
+> [!Note]
+> If a plugin is defined to have the location `page` the fragment should be on `RootQuery` and for `layout` it should be a fragment of `RenderedTemplate`.