Update contributing doc

[grbIzl]

I've added more details about current dev process.

Check list

• added or updated unit tests
• updated Astar official documentation
• added OnRuntimeUpgrade hook for precompile revert code registration
• added benchmarks & weights for any modified runtime logics.

[Dinonard]

Nice, thank you!

[github-actions]

Package	Line Rate	Branch Rate	Health
precompiles/substrate-ecdsa/src	67%	0%	➖
pallets/inflation/src	90%	0%	✔
precompiles/unified-accounts/src	100%	0%	✔
pallets/static-price-provider/src	91%	0%	✔
precompiles/xcm/src	69%	0%	➖
pallets/dapp-staking/src	79%	0%	➖
chain-extensions/types/assets/src	0%	0%	❌
pallets/ethereum-checked/src	76%	0%	➖
chain-extensions/types/unified-accounts/src	0%	0%	❌
pallets/xc-asset-config/src	48%	0%	❌
precompiles/assets-erc20/src	78%	0%	➖
pallets/vesting-mbm/src	87%	0%	✔
pallets/dapp-staking/rpc/runtime-api/src	0%	0%	❌
precompiles/sr25519/src	56%	0%	➖
primitives/src	54%	0%	➖
chain-extensions/unified-accounts/src	0%	0%	❌
pallets/dapp-staking/src/benchmarking	95%	0%	✔
pallets/astar-xcm-benchmarks/src/generic	100%	0%	✔
pallets/dapp-staking/src/test	0%	0%	❌
chain-extensions/pallet-assets/src	54%	0%	➖
pallets/collective-proxy/src	94%	0%	✔
precompiles/dapp-staking/src	89%	0%	✔
precompiles/dapp-staking/src/test	0%	0%	❌
precompiles/dispatch-lockdrop/src	83%	0%	✔
pallets/price-aggregator/src	76%	0%	➖
pallets/unified-accounts/src	81%	0%	✔
pallets/collator-selection/src	87%	0%	✔
pallets/astar-xcm-benchmarks/src	86%	0%	✔
pallets/dynamic-evm-base-fee/src	85%	0%	✔
primitives/src/xcm	62%	0%	➖
pallets/astar-xcm-benchmarks/src/fungible	100%	0%	✔
Summary	76% (3490 / 4605)	0% (0 / 0)	➖

Minimum allowed line rate is 50%