document "builder" files discussed in deploy-script-support README

[tgrecojs]

the README associated with the deploy-script-support package is a golden goose for those trying to deploy contracts on agoric. i am opening up this issue to signal that it may be beneficial to reference this within the documentation.

the "builder" files are particularly important to have knowledge of. they seem to play a crucial role in the deployment process for contracts that exist within the agoric-sdk, so i was surprised to have had to stumble upon this README for such crucial information