readme: add contribute section #632

Job	Run time
Format	22s
Clippy	50s
Tests	1m 49s
Docker (chain, chain)	9m 44s
Docker (governance, governance)	9m 46s
Validate Swagger	31s
Docker (pos, pos)	9m 32s
Docker (rewards, rewards)	9m 27s
Docker (seeder, seeder)	9m 25s
Docker (webserver, webserver)	10m 9s
Docker (parameters, parameters)	9m 25s
Docker (transactions, transactions)	9m 30s
can_enqueue	1s
can_merge	0s
	1h 20m 31s

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