Add README.

README.md

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+
+Puzzle Solver [![Version][version-img]][version-url] [![Status][travis-ci-img]][travis-ci-url]
+=============
+
+
+About
+-----
+
+Solve logic puzzles by simply describing the puzzle's rules as
+constraints.  This is suitable for solving puzzles with integer
+variables such as Sudoku.
+
+
+Examples
+--------
+
+A few example programs are provided in the `tests/` directory:
+
+* _Sudoku_ - https://en.wikipedia.org/wiki/Sudoku
+* _N-queens problem_ - https://en.wikipedia.org/wiki/Eight_queens_puzzle
+
+To clone this repository, run:
+
+```sh
+git clone https://github.com/wangds/puzzle-solver.git
+```
+
+Then build the library and run the test programs using Cargo.
+
+```sh
+cargo test --test sudoku -- --nocapture
+```
+
+
+Basic Usage
+-----------
+
+Add Puzzle Solver as a dependency to your project's Cargo.toml:
+
+```toml
+[dependencies]
+puzzle-solver = "0.1"
+```
+
+
+Documentation
+-------------
+
+* [Documentation][documentation].
+
+
+Author
+------
+
+David Wang
+
+
+[documentation]: https://docs.rs/puzzle-solver/
+[travis-ci-img]: https://travis-ci.org/wangds/puzzle-solver.svg?branch=master
+[travis-ci-url]: https://travis-ci.org/wangds/puzzle-solver
+[version-img]: https://img.shields.io/crates/v/puzzle-solver.svg
+[version-url]: https://crates.io/crates/puzzle-solver