update readme instructions to not add any other dependencies

[activescott]

it seems by just declaring the proper peer dependencies npm now will install it in the parent project ok?

[activescott]

at least it works in activescott/diag

[activescott]

so it worked locally without adding dependencies in node@16 but in a github actions with node@12 it failed without adding prettier, eslint, @typescript-eslint/eslint-plugin, eslint-config-prettier, @typescript-eslint/parser dev dependencies...