Document how different branches map to deploys

[samajammin]

My memory is fuzzy here - could we please document this somewhere in the READE? 😅

Perhaps we add something along these lines:

Development and deployment

By default, dev acts as the primary base branch which all PRs should merge into.

The exception to this rule is when deploying the Launchpad:

• Open a PR to merge dev into master to deploy a testnet Launchpad (e.g. Release dev -> master #517 for https://prater.launchpad.ethereum.org/ )
• Open a PR to merge master into mainnet to deploy the Mainnet Launchpad (e.g. Release master -> mainnet #518 for https://launchpad.ethereum.org/)

[samajammin]

@wackerow assigning to you. Could you please check my logic here? Feel free to make additions/edits & add this to the README.

Thanks in advance!