Add reader

reader.go

@@ -0,0 +1,20 @@
+package main
+
+import "golang.org/x/tour/reader"
+
+type MyReader struct{}
+
+// TODO: Add a Read([]byte) (int, error) method to MyReader.
+
+func (m MyReader) Read(b []byte) (int, error) {
+	cnt := 0
+	for i := range b {
+		b[i] = 'A'
+		cnt++
+	}
+	return cnt, nil
+}
+
+func main() {
+	reader.Validate(MyReader{})
+}