doc: Included instructions for Mac setup (poetry).

[waynchi]

• Poetry requires an env variable for Mac.
• See here: https://stackoverflow.com/questions/70003829/poetry-installed-but-poetry-command-not-found

[rbren]

🤔 this is the sort of stuff we're generally hesitant to add to the README (otherwise it becomes a heap of special cases for windows, M1, debian, etc etc)

Is there any way we could put this as an error message in the Makefile? Like if ! poetry --version; echo "put poetry in your path"

[anasdorbani]

@rbren do you mean something like that #801?

[neubig]

Ugh, sorry, I just noticed these two PRs. I sent my own solution here: https://github.com/OpenDevin/OpenDevin/pull/818

[anasdorbani]

@neubig provide an alternative solution which LGTM!