add README.md with example code

Author: terryh

README.md

@@ -0,0 +1,36 @@
+## gppdf
+golang wrap for wkhtmltopdf command.
+
+## Example
+
+```go
+package main
+
+import (
+    "fmt"
+    "net/http"
+
+    "github.com/terryh/gopdf"
+)
+
+func Pdfhandle(w http.ResponseWriter, r *http.Request) {
+    result, err := gopdf.Url2pdf("http://nvd3.org/examples/stackedArea.html")
+    fmt.Println(err)
+    w.Header().Set("Content-Type", "application/pdf")
+    w.Write(result)
+}
+
+func main() {
+
+    http.HandleFunc("/", Pdfhandle)
+
+    http.ListenAndServe(":8080", nil)
+
+}
+
+
+```
+
+
+
+