Fix the name of the zero-shot CoT approach

[fonfonx]

In Unit 1 the method described as ReAct does not correspond to the ReAct approach but to the Zero-shot Chain of Thought approach, as described in this paper https://arxiv.org/pdf/2205.11916 where the image illustrating the approach comes from (page 2).

ReAct is a more complex approach described in https://arxiv.org/pdf/2210.03629 which consists in forcing the LLM to alternate between Reasoning and Acting steps by using few-shot examples following this mechanism.