add blank line to make rst format correct

Author: jmitrevs

docs/reference.rst

@@ -90,6 +90,7 @@ Acknowledgments
 ===============
 If you benefited from participating in our community, we ask that you please acknowledge the Fast Machine Learning collaboration, and particular individuals who helped you, in any publications.
 Please use the following text for this acknowledgment:
+
   We acknowledge the Fast Machine Learning collective as an open community of multi-domain experts and collaborators. This community and \<names of individuals\>, in particular, were important for the development of this project.