Update README.md

Author: ocots

README.md

@@ -18,9 +18,9 @@
 The [OptimalControl.jl](https://juliahub.com/ui/Packages/General/OptimalControl) package is the root package of the [control-toolbox ecosystem](https://github.com/control-toolbox).
 The control-toolbox ecosystem gathers Julia packages for mathematical control and applications. It aims to provide tools to model and solve optimal control problems by direct and indirect methods.
 
-| **Documentation**  | **Code Status**  | **Release**  |
-|:-------------------|:-----------------|:-------------|
-| [![Documentation][doc-stable-img]][doc-stable-url] [![Documentation][doc-dev-img]][doc-dev-url] | [![Build Status][ci-img]][ci-url] [![Covering Status][co-img]][co-url] | [![Release][release-img]][release-url] |
+| **Documentation**  | **Code Status**  | **Release**  | **Citation** |
+|:-------------------|:-----------------|:-------------|:-------------|
+| [![Documentation][doc-stable-img]][doc-stable-url] [![Documentation][doc-dev-img]][doc-dev-url] | [![Build Status][ci-img]][ci-url] [![Covering Status][co-img]][co-url] | [![Release][release-img]][release-url] | [![DOI](https://zenodo.org/badge/541187171.svg)](https://zenodo.org/doi/10.5281/zenodo.13336563) |
 
 ## Installation