add CITATION.cff (#1174)

Author: HydrogenSulfate

CITATION.cff

@@ -0,0 +1,21 @@
+# This CITATION.cff file was generated with cffinit.
+# Visit https://bit.ly/cffinit to generate yours today!
+
+cff-version: 1.2.0
+title: PaddleScience
+message: >-
+  If you use this repository, please cite it using the metadata from this file.
+type: software
+authors:
+  - given-names: PaddleScience Authors
+repository-code: "https://github.com/PaddlePaddle/PaddleScience"
+repository: "https://github.com/PaddlePaddle/PaddleScience"
+keywords:
+  - machine-learning
+  - deep-learning
+  - supervised-learning
+  - paddlepaddle
+  - self-supervised-learning
+  - ai4science
+  - operator-learning
+license: Apache-2.0