chore: add DEV workflow instructions for librarian #2615

Job	Run time
filter	1m 7s
downstream-compatibility (java-pubsublite)	4m 20s
downstream-compatibility (java-firestore)	4m 24s
downstream-compatibility (spring-cloud-gcp)	13m 18s
downstream-compatibility (java-bigtable)	9m 18s
downstream-compatibility (java-pubsub)	4m 10s
conditional-required-check	2s
	36m 39s

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