Add lesson release citation/badge

Author: Chris Erdmann

README.md

@@ -1,3 +1,5 @@
+[![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.3265772.svg)](https://doi.org/10.5281/zenodo.3265772)  
+
 # Maintainers for Library Carpentry: Introduction to Git
 
 - [Silvia di Giorgio](https://twitter.com/digiorgiosilvia )
@@ -38,7 +40,7 @@ Library Carpentry is authored and maintained through issues, commits, and pull r
 
 ## Citation
 
-Library Carpentry: Introduction to Git. June 2016. https://librarycarpentry.org/lc-git/.
+Silvia di Giorgio (Ed.), Christopher Erdmann (Ed.), Thea Atwood (Ed.), Eric Lopatin (Ed.), Drew Heles (Ed.), Eva Seidlmayer (Ed.), Katrin Leinweber (Ed.), Belinda Weaver (Ed.), Jez Cope (Ed.), James Baker, Nora McGregor, Dan Michael O. Heggø, … Wolmar Nyberg Åkerström. (2019, July). LibraryCarpentry/lc-git: Library Carpentry: Introduction to Git, June 2019 (Version v2019.06.1). Zenodo. http://doi.org/10.5281/zenodo.3265772
 
 [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.3265772.svg)](https://doi.org/10.5281/zenodo.3265772)