include LICENSE file in crate (#12)

Summary:
Pull Request resolved: #12

Because of the `include=` directive, we need to explicitly include the license file as well or it won't end up in the generated crate.

Needed to package this in Fedora as a dependency of `difftastic`.

```
$ cargo package --allow-dirty --list | grep LICENSE
LICENSE
```

Reviewed By: edward-shen

Differential Revision: D89675738

fbshipit-source-id: f6f324ed4a3ceb563cab23924dede50f7294aecc

Author: michel-slm

Cargo.toml

@@ -10,6 +10,7 @@ version = "0.15.0"
 
 build = "bindings/rust/build.rs"
 include = [
+  "LICENSE",
   "bindings/rust/*",
   "grammar.js",
   "queries/*",