add doc

doc.go

@@ -0,0 +1,20 @@
+// Readline is a pure go implementation for GNU-Readline kind library.
+//
+// WHY: Readline will support most of features which GNU Readline is supported, and provide a pure go environment and a MIT license.
+//
+// example:
+// 	rl, err := readline.New("> ")
+// 	if err != nil {
+// 		panic(err)
+// 	}
+// 	defer rl.Close()
+//
+// 	for {
+// 		line, err := rl.Readline()
+// 		if err != nil { // io.EOF
+// 			break
+// 		}
+// 		println(line)
+// 	}
+//
+package readline