Docs: new documentation site (#2723)

This commit adds a VitePress build to the main repository,
aiming to ditch GitHub Wiki. Moving further, we're going to
host our own documentation site eithor on GitHub Pages or
something alike.

docs/premium/introduction.md

@@ -0,0 +1,26 @@
+---
+sidebarTitle: Introduction
+sidebarOrder: 1
+---
+
+# Introduction
+
+In the past, there was only one open-source version of Clash, until some [improper uses and redistributions](https://github.com/Dreamacro/clash/issues/541#issuecomment-672029110) of Clash arose. From that, we decided to fork Clash and develop the more advanced features in a private GitHub repository.
+
+Don't worry just yet - the Premium core will stay free of charge, and the security is enforced with peer reviews from multiple credible developers.
+
+## What's the difference?
+
+The Premium core is a fork of the open-source Clash core with the addition of the following features:
+
+- [TUN Device](/premium/tun-device) with the support of `auto-redir` and `auto-route`
+- [eBPF Redirect to TUN](/premium/ebpf)
+- [Rule Providers](/premium/rule-providers)
+- [Script](/premium/script)
+- [Script Shortcuts](/premium/script-shortcuts)
+- [Userspace Wireguard](/premium/userspace-wireguard)
+- [The Profiling Engine](/premium/the-profiling-engine)
+
+## Obtaining a Copy
+
+You can download the latest Clash Premium binaries from [GitHub Releases](https://github.com/Dreamacro/clash/releases/tag/premium).