chore(docs): update yarn installation command (heroui-inc#4132)

There is no `-g` flag in yarn. `global` is a command which must immediately follow yarn. 

Source: https://classic.yarnpkg.com/lang/en/docs/cli/global/

apps/docs/content/docs/guide/installation.mdx

@@ -26,7 +26,7 @@ Execute one of the following commands in your terminal:
 <PackageManagers
   commands={{
     npm: "npm install -g nextui-cli",
-    yarn: "yarn add -g nextui-cli",
+    yarn: "yarn global add nextui-cli",
     pnpm: "pnpm add -g nextui-cli",
     bun: "bun add -g nextui-cli",
   }}