Fix micro typo in README

[ShIRannx]

NOTE: You should not need to use pydantic-core directly, instead use pydantic which which in turn uses pydantic-core.
to
NOTE: You should not need to use pydantic-core directly; instead, use pydantic, which in turn uses pydantic-core.

Selected Assignee: @dmontagu

[davidhewitt]

Closed in #738