Update composition-api-introduction.md (#832)

Alex-Sokolov · web-flow · commit e7c380d24b7d · 2021-01-30T22:06:34.000+01:00
diff --git a/src/guide/composition-api-introduction.md b/src/guide/composition-api-introduction.md
@@ -309,7 +309,7 @@ export default {
 }
 ```
 
-For more details on `watch`, refer to our [in-depth guide]().
+For more details on `watch`, refer to our [in-depth guide](reactivity-computed-watchers.md#watch).
 
 **Let’s now apply it to our example:**
 
