docs: add component comments (#7376)

* docs: add component comments

* Review: copy on IDE

Co-authored-by: Ben McCann <322311+benmccann@users.noreply.github.com>

* Review: conventions/brevity

Co-authored-by: Ben McCann <322311+benmccann@users.noreply.github.com>

---------

Co-authored-by: Ben McCann <322311+benmccann@users.noreply.github.com>

Author: metonym

documentation/docs/02-template-syntax/02-basic-markup.md

@@ -138,3 +138,12 @@ Comments beginning with `svelte-ignore` disable warnings for the next block of m
 <!-- svelte-ignore a11y-autofocus -->
 <input bind:value={name} autofocus />
 ```
+
+You can document components with the `@component` tag. These comments will appear when hovering over a component in IDEs with support such as VS Code with [the Svelte VS Code extension](https://marketplace.visualstudio.com/items?itemName=svelte.svelte-vscode).
+
+```svelte
+<!--
+@component this is a component description
+-->
+<h1>Hello world</h1>
+```