fix(a11y): add title to copy code button (#1437)

Co-authored-by: Divyansh Singh <40380293+brc-dd@users.noreply.github.com>

src/node/markdown/plugins/preWrapper.ts

@@ -15,7 +15,7 @@ export const preWrapperPlugin = (md: MarkdownIt) => {
     const [tokens, idx] = args
     const lang = tokens[idx].info.trim().replace(/-vue$/, '')
     const rawCode = fence(...args)
-    return `<div class="language-${lang}"><button class="copy"></button><span class="lang">${
+    return `<div class="language-${lang}"><button title="Copy Code" class="copy"></button><span class="lang">${
       lang === 'vue-html' ? 'template' : lang
     }</span>${rawCode}</div>`
   }