Add apache-2.0 LICENSE
Add apache-2.0 LICENSE

`apache-2.0` is a permissive license.

It happens to be the same license used by both [bazel](https://github.com/bazelbuild/bazel/blob/master/LICENSE) and [rules_python](https://github.com/bazelbuild/rules_python/blob/master/LICENSE)
bazelbuild/rules_python,bazelbuild/rules_python,bazelbuild/rules_python