doc: Require Python3.8 to sapp

[WangGithubUser]

Pre-submission checklist

• [x] I've ran the linters locally and fixed lint errors related to the files I modified in this PR. You can install the linters by running pip install -r requirements-dev.txt && pre-commit install
• [x] pre-commit run

Summary

sapp require Python3.8 since facebook/sapp@27b4220789a97045a879e4a9e51d6a26751675ec

Test Plan

N/A

[kinto0]

it seems like the docs say 3.7?

https://pypi.org/project/fb-sapp/#:~:text=To%20run%20SAPP%2C%20you%20will%20need%20Python%203.7%20or%20later.

[WangGithubUser]

https://github.com/facebook/sapp/blob/main/README.md?plain=1#L17 The pypi page is outdated.

[facebook-github-bot]

@alexkassil has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@alexkassil merged this pull request in facebook/pyre-check@689a8bed35d3ab2a134a9bfb0c49845764760361.