vendor: add github.com/a8m/tree

vendor/github.com/a8m/tree/README.md

@@ -0,0 +1,41 @@
+tree [![Build status][travis-image]][travis-url] [![License][license-image]][license-url]
+---
+> An implementation of the [`tree`](http://mama.indstate.edu/users/ice/tree/) command written in Go, that can be used  programmatically.
+
+#### Installation:
+```sh
+$ go get github.com/a8m/tree/cmd/tree
+```
+
+#### How to use `tree` programmatically ?
+You can take a look on [`cmd/tree`](https://github.com/a8m/tree/blob/master/cmd/tree/tree.go), and [s3tree](http://github.com/a8m/s3tree) or see the example below.
+```go
+import (
+    "github.com/a8m/tree"
+)
+
+func main() {
+    opts := &tree.Options{
+        // Fs, and OutFile are required fields.
+        // fs should implement the tree file-system interface(see: tree.Fs),
+        // and OutFile should be type io.Writer
+        Fs: fs,
+        OutFile: os.Stdout,
+        // ...
+    }
+    inf.New("root-dir")
+    // Visit all nodes recursively
+    inf.Visit(opts)
+    // Print nodes 
+    inf.Print(opts)
+}
+```
+
+### License
+MIT
+
+
+[travis-image]: https://img.shields.io/travis/a8m/tree.svg?style=flat-square
+[travis-url]: https://travis-ci.org/a8m/tree
+[license-image]: http://img.shields.io/npm/l/deep-keys.svg?style=flat-square
+[license-url]: LICENSE