add badge

Author: 0b01

README.md

@@ -1,5 +1,6 @@
 # tectonicdb
 
+[![build](https://github.com/0b01/tectonicdb/workflows/Rust/badge.svg)](https://github.com/0b01/tectonicdb/actions?query=workflow%3ARust)
 [![crate.io](https://img.shields.io/crates/v/tdb-core.svg)](https://crates.io/crates/tdb-core)
 [![doc.rs](https://docs.rs/tdb_core/badge.svg)](https://docs.rs/crate/tdb_core)
 ![Minimum Rust version](https://img.shields.io/badge/rustc-1.40+-yellow.svg)