docs: add CITATION.cff

CITATION.cff

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+# This CITATION.cff file was generated with cffinit.
+# Visit https://bit.ly/cffinit to generate yours today!
+
+cff-version: 1.2.0
+title: Ramachandraw
+version: 1.0.1
+message: >-
+  If you use this software, please cite it using the
+  metadata from this file.
+type: software
+authors:
+  - given-names: Alexandre
+    family-names: Dias Cirilo
+repository-code: 'https://github.com/alxdrcirilo/ramachandraw'
+repository-artifact: 'https://pypi.org/project/ramachandraw/'
+abstract: Ramachandran plotting tool.
+keywords:
+  - bioinformatics
+  - ramachandran
+  - protein structure
+license: MIT