Added a missing article

For grammatical correctness

src/guide/introduction.md

@@ -207,7 +207,7 @@ export default {
 
 ### Composition API {#composition-api}
 
-With Composition API, we define a component's logic using imported API functions. In SFCs, Composition API is typically used with [`<script setup>`](/api/sfc-script-setup). The `setup` attribute is a hint that makes Vue perform compile-time transforms that allow us to use Composition API with less boilerplate. For example, imports and top-level variables / functions declared in `<script setup>` are directly usable in the template.
+With Composition API, we define a component's logic using imported API functions. In SFCs, Composition API is typically used with [`<script setup>`](/api/sfc-script-setup). The `setup` attribute is a hint that makes Vue perform compile-time transforms that allow us to use the Composition API with less boilerplate. For example, imports and top-level variables / functions declared in `<script setup>` are directly usable in the template.
 
 Here is the same component, with the exact same template, but using Composition API and `<script setup>` instead: