docs(useClipboard): update demo and type fixes (#2430)

* docs: update copy() method to include argument.
* docs: update useClipboard demo to be more detailed and self-explanatory

Co-authored-by: wheat <jacobrclevenger@gmail.com>

packages/core/useClipboard/index.md

@@ -18,11 +18,19 @@ const { text, copy, copied, isSupported } = useClipboard({ source })
 ```
 
 ```html
-<button @click='copy()'>
-  <!-- by default, `copied` will be reset in 1.5s -->
-  <span v-if='!copied'>Copy</span>
-  <span v-else>Copied!</span>
-</button>
+ <div v-if="isSupported">
+    <button @click='copy(source)'>
+      <!-- by default, `copied` will be reset in 1.5s -->
+      <span v-if='!copied'>Copy</span>
+      <span v-else>Copied!</span>
+    </button>
+    <p>
+      Current copied: <code>{{ text || 'none' }}</code>
+    </p>
+  </div>
+  <p v-else>
+    Your browser does not support Clipboard API
+  </p>
 ```
 
 Set `legacy: true` to keep the ability to copy if [Clipboard API](https://developer.mozilla.org/en-US/docs/Web/API/Clipboard_API) is not available. It will handle copy with [execCommand](https://developer.mozilla.org/en-US/docs/Web/API/Document/execCommand) as fallback.