add citation

CITATION.cff

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+cff-version: 1.2.0
+message: "If you use this software, please cite it as below."
+authors:
+  - family-names: Orban
+    given-names: Dominique
+    orcid: https://orcid.org/0000-0002-8017-7687
+  - name: "contributors"
+title: "AMD.jl: A Julia interface to the AMD library of Amestoy, Davis and Duff"
+identifiers:
+  - description: "The concept DOI of the work."
+    type: doi
+    value: 10.5281/zenodo.3381898
+  - description: "The versioned DOI for version 0.4.0 of the work."
+    type: doi
+    value: 10.5281/zenodo.3783808
+doi: 10.5281/zenodo.3381898
+date-released: 2020-May
+license: Mozilla Public License 2.0
+repository-code: "https://github.com/JuliaSmoothOptimizers/AMD.jl"