Added zenodo badge

README.md

@@ -1,4 +1,20 @@
 # Epigrass
+If you use epigrass in your research, please use the following DOI to cite it:
+
+[![DOI](https://zenodo.org/badge/59497476.svg)](https://zenodo.org/badge/latestdoi/59497476)
+or this bibtex entry.
+```bibtex
+@software{flavio_codeco_coelho_2021_4554753,
+  author       = {Flávio Codeço Coelho},
+  title        = {fccoelho/epigrass: COVID19},
+  month        = feb,
+  year         = 2021,
+  publisher    = {Zenodo},
+  version      = {v3.0.2},
+  doi          = {10.5281/zenodo.4554753},
+  url          = {https://doi.org/10.5281/zenodo.4554753}
+}
+```
 ## Epidemiological Geo-referenced Analysis and Simulation system
 ![dashboard](docs/source/dashboard2.png)
 Epigrass is a Python Library aimed at making the simulation of metapopulation models as easy as possible.