re-add root README.md

Now that he main README moved into the gitlab-runner crate re-add a
small README at the root

Signed-off-by: Sjoerd Simons <sjoerd@collabora.com>

README.md

@@ -0,0 +1,24 @@
+# Rust crate to build custom gitlab runners
+
+[![Crates.io][crates-badge]][crates-url]
+[![Documentation][docs-badge]][docs-url]
+[![MIT/Apache-2 licensed][license-badge]][license-url]
+[![Build Status][actions-badge]][actions-url]
+
+[crates-badge]: https://img.shields.io/crates/v/gitlab-runner
+[crates-url]: https://crates.io/crates/gitlab-runner
+[docs-badge]: https://docs.rs/gitlab-runner/badge.svg
+[docs-url]: https://docs.rs/gitlab-runner
+[license-badge]: https://img.shields.io/badge/license-MIT_OR_Apache--2-blue.svg
+[license-url]: LICENSE-APACHE
+[actions-badge]: https://github.com/collabora/gitlab-runner-rs/workflows/CI/badge.svg
+[actions-url]:https://github.com/collabora/gitlab-runner-rs/actions?query=workflow%3ACI
+
+
+[Gitlab](https://gitlab.com) provides a REST style API for CI runners. These
+crates abstract this API away so custom runners can easily be build without
+any knowledge of the gitlab APIs
+
+This workspace consists of two crates:
+* [gitlab-runner](gitlab-runner/README.md) - Main runner crate
+* gitlab-runner-mock - Mock crate for the gitlab runner APIs