favicon for docs #958

Job	Run time
linux-64-py3.10	5m 51s
estimation_mode_test	16m 32s
macOS	6m 5s
develop-docbuild	0s
prototype_mtc	43m 17s
win-64	10m 13s
placeholder_psrc	35m 59s
Standard 1-Zone Example (MTC)	5m 51s
random_seed_generation_test	2m 36s
prototype_marin	1m 32s
Standard 2-Zone Example (SANDAG)	1h 0m 40s
prototype_mtc_extended	1h 18m 28s
placeholder_sandag	1h 33m 42s
prototype_sandag_xborder	4m 23s
production_semcog	5m 3s
prototype_mwcog	42m 56s
placeholder_multiple_zone	7m 52s
	7h 1m 0s

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