added godoc comments and license notes for the gocloud.dev vendored code

tools/filesystem/blob/reader.go

@@ -8,6 +8,24 @@ import (
 	"time"
 )
 
+// Largely copied from gocloud.dev/blob.Reader to minimize breaking changes.
+//
+// -------------------------------------------------------------------
+// Copyright 2019 The Go Cloud Development Kit Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// -------------------------------------------------------------------
+
 var _ io.ReadSeekCloser = (*Reader)(nil)
 
 // Reader reads bytes from a blob.