Update citation

CITATION.cff

@@ -3,10 +3,19 @@
 
 cff-version: 1.2.0
 title: Ruffini
-message: Computations over algebraic structures in Java made easy
+message: >-
+  If you use this software, please cite it using the
+  metadata from this file.
 type: software
 authors:
   - given-names: Jonas
     family-names: Lindstrøm
     email: [email protected]
     orcid: 'https://orcid.org/0000-0002-1989-3019'
+repository-code: 'https://github.com/jonas-lj/Ruffini'
+abstract: Computations over algebraic structures in Java made easy
+keywords:
+  - Algebra
+  - Java
+  - Crypotography
+license: MIT