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/advanced-usages/golang-api.md

@@ -0,0 +1,59 @@
+---
+sidebarTitle: Integrating Clash in Golang Programs
+sidebarOrder: 3
+---
+
+# Integrating Clash in Golang Programs
+
+If clash does not fit your own usage, you can use Clash in your own Golang code.
+
+There is already basic support:
+
+```go
+package main
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net"
+
+	"github.com/Dreamacro/clash/adapter/outbound"
+	"github.com/Dreamacro/clash/constant"
+	"github.com/Dreamacro/clash/listener/socks"
+)
+
+func main() {
+	in := make(chan constant.ConnContext, 100)
+	defer close(in)
+
+	l, err := socks.New("127.0.0.1:10000", in)
+	if err != nil {
+		panic(err)
+	}
+	defer l.Close()
+
+	println("listen at:", l.Address())
+
+	direct := outbound.NewDirect()
+
+	for c := range in {
+		conn := c
+		metadata := conn.Metadata()
+		fmt.Printf("request incoming from %s to %s\n", metadata.SourceAddress(), metadata.RemoteAddress())
+		go func () {
+			remote, err := direct.DialContext(context.Background(), metadata)
+			if err != nil {
+				fmt.Printf("dial error: %s\n", err.Error())
+				return
+			}
+			relay(remote, conn.Conn())
+		}()
+	}
+}
+
+func relay(l, r net.Conn) {
+	go io.Copy(l, r)
+	io.Copy(r, l)
+}
+```