Improve README with cargo instructions

Author: steveklabnik

README.md

@@ -4,3 +4,22 @@ glob
 Support for matching file paths against Unix shell style patterns.
 
 ![[Build Status](https://travis-ci.org/rust-lang/glob.svg?branch=master)](https://travis-ci.org/rust-lang/glob)
+
+## Usage
+
+To use `glob`, add this to your `Cargo.toml`:
+
+```toml
+[dependencies.glob]
+
+git = "https://github.com/rust-lang/glob.git"
+```
+
+And add this to your crate root:
+
+```rust
+#![feature(macro_rules)]
+extern crate glob;
+use glob::glob;
+```
+