Update README

README.md

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 # rust-ico
-Rust library for encoding/decoding ICO image files
+
+A pure Rust library for encoding/decoding
+[ICO image files](https://en.wikipedia.org/wiki/ICO_%28file_format%29).
+
+Documentation: https://docs.rs/ico/
+
+## Overview
+
+An ICO file (.ico) stores a collection of small images of different sizes and
+color depths (up to 256x256 pixels each).  Individial images within the file
+can be encoded in either BMP or PNG format.  ICO files are typically used for
+website favicons and for Windows application icons.
+
+CUR files (.cur), which store Windows cursor images, use the same file format
+as ICO files, except that each image also comes with (x, y) *hotspot*
+coordinates that determines where on the image the user is pointing.  This
+libary supports both file types.
+
+## License
+
+rust-ico is made available under the
+[MIT License](http://spdx.org/licenses/MIT.html).