Create CITATION.cff (#329)

CITATION.cff

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+cff-version: 1.2.0
+message: "If this software contributes to published work, please cite smartcore."
+type: software
+title: "smartcore: Machine Learning in Rust"
+abstract: "smartcore is a comprehensive machine learning and numerical computing library for Rust, offering supervised and unsupervised algorithms, model evaluation tools, and linear algebra abstractions, with optional ndarray integration." [web:5][web:3]
+repository-code: "https://github.com/smartcorelib/smartcore" [web:5]
+url: "https://github.com/smartcorelib" [web:3]
+license: "MIT" [web:13]
+keywords:
+  - Rust
+  - machine learning
+  - numerical computing
+  - linear algebra
+  - classification
+  - regression
+  - clustering
+  - SVM
+  - Random Forest
+  - XGBoost [web:5]
+authors:
+  - name: "smartcore Developers" [web:7]
+  - name: "Lorenzo (contributor)" [web:16]
+  - name: "Community contributors" [web:7]
+version: "0.4.2" [attached_file:1]
+date-released: "2025-09-14" [attached_file:1]
+preferred-citation:
+  type: software
+  title: "smartcore: Machine Learning in Rust"
+  authors:
+    - name: "smartcore Developers" [web:7]
+  url: "https://github.com/smartcorelib" [web:3]
+  repository-code: "https://github.com/smartcorelib/smartcore" [web:5]
+  license: "MIT" [web:13]
+references:
+  - type: manual
+    title: "smartcore Documentation"
+    url: "https://docs.rs/smartcore" [web:5]
+  - type: webpage
+    title: "smartcore Homepage"
+    url: "https://github.com/smartcorelib" [web:3]
+notes: "For development features, see the docs.rs page and the repository README; SmartCore includes algorithms such as SVM, Random Forest, K-Means, PCA, DBSCAN, and XGBoost." [web:5]