Update README.md

Author: j-wags

README.md

@@ -28,8 +28,8 @@ Details for each force field in this repository can be found in the following ta
 
 | Filename                                    | DOI                                                                                                       | FF line | Release Date  | Major format changes? |
 |---------------------------------------------|-----------------------------------------------------------------------------------------------------------|---------|---------------|-----------------------|
-| `openff-2.1.1.offxml`                       |                                                                                                           | Sage    | Jan 22, 2024  | No                    |
-| `openff_unconstrained-2.1.1.offxml`         |                                                                                                           | Sage    | Jan 22, 2024  | No                    |
+| `openff-2.1.1.offxml`                       | [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.10553473.svg)](https://doi.org/10.5281/zenodo.10553473) | Sage    | Jan 22, 2024  | No                    |
+| `openff_unconstrained-2.1.1.offxml`         | [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.10553473.svg)](https://doi.org/10.5281/zenodo.10553473) | Sage    | Jan 22, 2024  | No                    |
 | `tip5p-1.0.0.offxml`                        | see `docs/water-models.md`                                                                                | Ports   | Nov 6, 2023   | No                    |
 | `spce-1.0.0.offxml`                         | see `docs/water-models.md`                                                                                | Ports   | Nov 6, 2023   | No                    |
 | `tip4p_ew-1.0.0.offxml`                     | see `docs/water-models.md`                                                                                | Ports   | Nov 6, 2023   | No                    |