add citation to readme and dataset info

README.md

@@ -106,3 +106,16 @@ which has opened my eyes to a new world of cybersecurity modeling.
 
 If you are a cybersecurity expert please consider [contributing to
 D3FEND](https://d3fend.mitre.org/contribute/).
+
+[D3FEND Resources](https://d3fend.mitre.org/resources/)
+
+### Citation
+```bibtex
+@techreport{kaloroumakis2021d3fend,
+  title={Toward a Knowledge Graph of Cybersecurity Countermeasures},
+  author={Kaloroumakis, Peter E. and Smith, Michael J.},
+  institution={The MITRE Corporation},
+  year={2021},
+  url={https://d3fend.mitre.org/resources/D3FEND.pdf}
+}
+```

d3fend.py

@@ -15,6 +15,13 @@ class D3FENDDatasetBuilder(GeneratorBasedBuilder):
             description="D3FEND is a framework which encodes a countermeasure knowledge base as a knowledge graph. The graph contains the types and relations that define key concepts in the cybersecurity countermeasure domain and the relations necessary to link those concepts to each other. Each of these concepts and relations are linked to references in the cybersecurity literature.",
             homepage="https://d3fend.mitre.org/",
             license="MIT",
+            citation=r"""@techreport{kaloroumakis2021d3fend,
+  title={Toward a Knowledge Graph of Cybersecurity Countermeasures},
+  author={Kaloroumakis, Peter E. and Smith, Michael J.},
+  institution={The MITRE Corporation},
+  year={2021},
+  url={https://d3fend.mitre.org/resources/D3FEND.pdf}
+}""",
             features=Features({
                 'subject': Value('string'),
                 'predicate': Value('string'),