chore: add DEV workflow instructions for librarian #19345

Job	Run time
generate-readme	1m 19s
gitignore_correctness	1m 14s
owlbot-py	1m 24s
owlbot-yaml	1m 6s
package_name_check	1m 7s
group_id_check_for_maps_libraries	9m 6s
root-pom	1m 55s
gapic-bom	1m 51s
	19m 2s

Provide feedback