readme for filetreelist

Author: Stephan Dilly

filetreelist/README.md

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+# filetreelist
+
+This crate is designed as part of the [gitui](http://gitui.org) project.
+
+`filetreelist` provides a very common functionality of `gitui`: lists of files visualized as a tree. It allows efficient iteration of only the visual (non collapsed) elements and change the tree state correctly given well defined inputs like `Up`/`Down`/`Collapse`.
+
+It is the main driver behind the file tree feature:
+
+![demo](demo.gif)