Add citation as CFF file.

[skip ci]

Author: maleadt

Diff for: CITATION.bib

@@ -0,0 +1,34 @@
+cff-version: 1.2.0
+message: If you use CUDA.jl in your work, please cite it using the following metadata
+title: CUDA.jl
+abstract: This package provides CUDA programming support for the Julia programming language
+authors:
+- family-names: Besard
+  given-names: Tim
+  affiliation: Julia Computing
+keywords:
+- julia
+- cuda
+version: 3.3.4
+date-released: 2021--7-15
+license: MIT
+repository-code: https://github.com/JuliaGPU/CUDA.jl/
+
+references:
+  - type: article
+    authors:
+      - family-names: Besard
+        given-names: Tim
+        affiliation: "Ghent University"
+        orcid: "https://orcid.org/0000-0001-7826-8021"
+      - family-names: Foket
+        given-names: Christophe
+      - family-names: "De Sutter"
+        given-names: Bjorn
+        affiliation: "Ghent University"
+        orcid: "https://orcid.org/0000-0003-0317-2089"
+    title: "Effective Extensible Programming: Unleashing Julia on GPUs"
+    journal: "IEEE Transactions on Parallel and Distributed Systems"
+    issn: "1045-9219"
+    year: 2018
+    doi: "10.1109/TPDS.2018.2872064"