Add a README.

README.md

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+# Org-Mode AST Investigation Tool
+This repository contains a slapdash tool to make visualizing the abstract syntax tree of an org-mode document easier. Write your org-mode source into the top text box, and below on the right it will create a clickable tree of the AST. When you click on a node, the contents of that node will be highlighted on the left.
+
+![Screenshot showing the interface to the org-mode abstract syntax tree investigation tool.](readme/screenshot.png?raw=true "Org-mode investigation tool interface")
+
+## Running
+TODO