Add repo status badge to README

Author: bgroenks96

README.md

@@ -1,6 +1,7 @@
 # CryoGrid.jl
 
 [![][docs-dev-img]][docs-dev-url]
+[![Project Status: Inactive – The project has reached a stable, usable state but is no longer being actively developed; support/maintenance will be provided as time allows.](https://www.repostatus.org/badges/latest/inactive.svg)](https://www.repostatus.org/#inactive)
 
 [docs-dev-img]: https://img.shields.io/badge/docs-latest-blue.svg
 [docs-dev-url]: https://cryogrid.github.io/CryoGrid.jl/dev/