Add non-submodule vendor directory.

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vendor/docdown/README.md

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+# Docdown <sup>v1.0.0-pre</sup>
+
+A simple JSDoc to Markdown documentation generator.
+
+## Documentation
+
+The documentation for Docdown can be viewed here: [/doc/README.md](https://github.com/jdalton/docdown/blob/master/doc/README.md#readme)
+
+For a list of upcoming features, check out our [roadmap](https://github.com/jdalton/docdown/wiki/Roadmap).
+
+## Installation and usage
+
+Usage example:
+
+~~~ php
+require("docdown.php");
+
+// generate Markdown
+$markdown = docdown(array(
+  "path" => $filepath,
+  "url"  => "https://github.com/username/project/blob/master/my.js"
+));
+~~~
+
+## Cloning this repo
+
+To clone this repository just use:
+
+~~~ bash
+git clone https://github.com/docdown/docdown.git
+cd docdown
+~~~
+
+Feel free to fork and send pull requests if you see improvements!
+
+## Author
+
+* [John-David Dalton](http://allyoucanleet.com/)
+  [![twitter/jdalton](http://gravatar.com/avatar/299a3d891ff1920b69c364d061007043?s=70)](https://twitter.com/jdalton "Follow @jdalton on Twitter")
+
+## Contributors
+
+* [Mathias Bynens](http://mathiasbynens.be/)
+  [![twitter/mathias](http://gravatar.com/avatar/24e08a9ea84deb17ae121074d0f17125?s=70)](https://twitter.com/mathias "Follow @mathias on Twitter")