fix: Add upgrade doc and fix variable description #338

Job	Run time
Collect workflow inputs	3s
Max TF pre-commit	1m 15s
Min TF pre-commit (.)	16s
Min TF pre-commit (./examples/s3-import-mysql)	22s
Min TF pre-commit (./examples/blue-green-deployment)	20s
Min TF pre-commit (./examples/enhanced-monitoring)	21s
Min TF pre-commit (./examples/cross-region-replica-postgres)	20s
Min TF pre-commit (./examples/replica-mysql)	24s
Min TF pre-commit (./examples/replica-postgres)	18s
Min TF pre-commit (./examples/complete-mysql)	23s
Min TF pre-commit (./examples/groups)	21s
Min TF pre-commit (./examples/complete-oracle)	23s
Min TF pre-commit (./examples/role-association-postgres)	23s
Min TF pre-commit (./examples/complete-mssql)	23s
Min TF pre-commit (./examples/complete-postgres)	21s
Min TF pre-commit (./modules/db_subnet_group)	22s
Min TF pre-commit (./modules/db_instance)	16s
Min TF pre-commit (./modules/db_instance_role_association)	20s
Min TF pre-commit (./modules/db_instance_automated_backups_replication)	18s
Min TF pre-commit (./modules/db_option_group)	15s
Min TF pre-commit (./modules/db_parameter_group)	17s
	7m 41s

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