Added Citations file

CITATION.cff

+cff-version: 1.2.0
+message: "If you want to cite the framework, feel free to use this"
+title: "pytorch-widedeep: A flexible package for multimodal deep learning"
+abstract: "A flexible package for multimodal-deep-learning to combine tabular data with text and images using Wide and Deep models in Pytorch."
+authors:
+  - name: Javier Rodriguez Zaurin
+    orcid: 0000-0002-1082-1107
+  - name: Pavol Mulinka
+    orcid: 0000-0002-9394-8794
+license: "Apache-2.0 and MIT"
+url: "https://pytorch-widedeep.readthedocs.io/en/latest/index.html"
+repository-code: "https://github.com/jrzaurin/pytorch-widedeep/"
+date-released: 2022-05-18
+keywords:
+  - Python
+  - Pytorch
+  - Deep learning