add: Go function example (tf-go-hello-fn)

examples/go-hello/code/main.go

@@ -0,0 +1,11 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+)
+
+func Handler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "text/plain")
+	fmt.Fprintf(w, "Hello from Go in Fission")
+}