docs: avoid duplicate vp installation in onboarding prompt (#2291)

Closes #2290

Co-authored-by: MK (fengmk2) <fengmk2@gmail.com>

Author: Arcadi4

docs/.vitepress/theme/components/CopyPrompt.vue

@@ -9,7 +9,7 @@ const DEFAULT_PROMPT = `I want to use Vite+ in my project. Vite+ is the unified
 
 First, read https://viteplus.dev/llms-full.txt to learn Vite+'s commands and configuration.
 
-Install the \`vp\` CLI:
+Install the \`vp\` CLI if it's not already on the system:
 - macOS / Linux: curl -fsSL https://vite.plus | bash
 - Windows (PowerShell): irm https://vite.plus/ps1 | iex