docs: Add copy button for code blocks (#715)

docs/package.json

@@ -15,6 +15,7 @@
   },
   "license": "MIT",
   "devDependencies": {
+    "@xiaopanda/vuepress-plugin-code-copy": "^1.0.3",
     "gh-pages": "^3.1.0",
     "vuepress": "^1.5.3",
     "vuepress-plugin-dehydrate": "^1.1.5",

docs/src/.vuepress/config.js

@@ -97,5 +97,6 @@ module.exports = {
     "dehydrate",
     "@vuepress/plugin-back-to-top",
     "@vuepress/plugin-medium-zoom",
+    "@xiaopanda/vuepress-plugin-code-copy",
   ],
 };