Add CITATION.cff file for academic referencing #1019

Job	Run time
linux-64-py	5m 38s
macOS	6m 57s
win-64	9m 12s
estimation_edb_creation_test	7m 32s
placeholder_psrc	51m 0s
prototype_marin	1m 47s
prototype_mtc	53m 30s
prototype_sandag_xborder	5m 58s
production_semcog	6m 59s
random_seed_generation_test	3m 28s
prototype_mtc_extended	1h 21m 58s
placeholder_sandag	2h 34m 16s
prototype_mwcog	50m 25s
placeholder_multiple_zone	10m 57s
Standard 2-Zone Example (SANDAG)	1h 18m 15s
Standard 1-Zone Example (MTC)	47m 9s
Estimation Mode Unit Tests	25m 16s
Estimation Notebooks Test	1h 0m 17s
Expression Profiling Tests	7m 36s
develop-docbuild	0s
	11h 8m 10s

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