Improve the documentation

[hackfisher]

• yarn add @darwinia/api-options should be yarn add @darwinia/types

• 50

• List well known projects which are using darwinia.js, including
  • Darwinia apps
  • wormhole-ui
  • https://github.com/polkadot-js/apps/tree/master/packages/apps-config
  • https://github.com/darwinia-network/staking-payouts
  • Subquery projects.
• Improve readability and clarity

[cinlk]

• yarn add @darwinia/api-options should be yarn add @darwinia/types
• Improve key packages description #50

• List well known projects which are using darwinia.js, including

  • Darwinia apps
  • wormhole-ui
  • https://github.com/polkadot-js/apps/tree/master/packages/apps-config
  • https://github.com/darwinia-network/staking-payouts
  • Subquery projects.
• Improve readability and clarity

done in #55