CONTRIBUTING: Clarifies Ref<X> syntax #214

Job	Run time
Compile / Installs platform (4) / Platform	16s
Compile / Installs platform (5) / Platform	18s
Compile / Installs platform (4) / Clean-up	0s
Compile / Installs platform (5) / Clean-up	0s
Compile / Compile (4)	21s
Compile / Compile (5)	27s
Compile / Clean-up	0s
Test (Collection.test, 5)	3m 14s
Test (Database.test, 5)	3m 29s
Test (DateTime.test, 5)	3m 56s
Test (ItemsHistory.test, 5)	3m 28s
Test (Object.test, 5)	3m 16s
Test (Redis.test, 5)	3m 29s
Test (ValueStorage.test, 5)	3m 35s
Clean-up / Clean-up	4s
	25m 53s

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