docs: add citation link (#2007)

CITATION.cff

@@ -0,0 +1,24 @@
+cff-version: 1.2.0
+message: "If you use this software, please cite it as below."
+authors:
+- family-names: "Packer"
+  given-names: "Charles"
+- family-names: "Wooders"
+  given-names: "Sarah"
+- family-names: "Lin"
+  given-names: "Kevin"
+- family-names: "Fang"
+  given-names: "Vivian"
+- family-names: "Patil"
+  given-names: "Shishir G"
+- family-names: "Stoica"
+  given-names: "Ion"
+- family-names: "Gonzalez"
+  given-names: "Joseph E"
+title: "MemGPT: Towards LLMs as Operating Systems"
+type: article
+journal: "arXiv preprint arXiv:2310.08560"
+year: 2023
+identifiers:
+  - type: arxiv
+    value: "2310.08560"