Add abstract to CITATION.cff

CITATION.cff

@@ -252,6 +252,14 @@ authors:
   affiliation: "Potsdam Institute for Climate Impact Research"
 
 title: REMIND - REgional Model of INvestments and Development
+abstract: REMIND (REgional Model of Investment and Development) is a numerical
+  open source model that represents the future evolution of the world economies
+  with a special focus on the development of the energy sector and the implications
+  for our world climate. The goal of REMIND is to find the optimal mix of investments
+  in the economy and the energy sectors of each model region given a set of population,
+  technology, policy and climate constraints. It also accounts for regional trade 
+  characteristics on goods, energy fuels, and emissions allowances. All greenhouse 
+  gas emissions due to human activities are represented in the model.
 version: "3.3.0.dev189"
 date-released: 2024-05-22
 repository-code: https://github.com/remindmodel/remind