README: How support C and Python

README.md

@@ -27,6 +27,45 @@ LLGo := Go + C + Python
 LLGo is compatible with C and Python through the language's **Application Binary Interface (ABI)**, while LLGo is compatible with Go through its **syntax (source code)**.
 
 
+## How support C and Python
+
+LLGo use `go:linkname` to link an extern symbol througth its **Application Binary Interface (ABI)**:
+
+```go
+import _ "unsafe" // for go:linkname
+
+//go:linkname Sqrt C.sqrt
+func Sqrt(x float64) float64
+```
+
+You can directly integrate it into [your own code](_demo/linkname/linkname.go):
+
+```go
+package main
+
+import _ "unsafe" // for go:linkname
+
+//go:linkname Sqrt C.sqrt
+func Sqrt(x float64) float64
+
+func main() {
+	println("sqrt(2) =", Sqrt(2))
+}
+```
+
+Or put it into a package (see [c/math](c/math/math.go)):
+
+```go
+package main
+
+import "github.com/goplus/llgo/c/math"
+
+func main() {
+	println("sqrt(2) =", math.Sqrt(2))
+}
+```
+
+
 ## C/C++ standard libary support
 
 You can import a C/C++ standard library in LLGo!