docs: update M1 docs

Created by: chrismwendt

I wasn't able to run E2E tests by setting PUPPETEER_EXECUTABLE_PATH. I tried:

• os.arch = () => 'x64' - error because os.arch is a getter
• "noImplicitUseStrict": true in tsconfig.json - allows the previous line, but had no effect, os.arch() still returns 'arm64'
• Object.defineProperty(os, 'arch', () => 'x64') - same, had no effect

@varungandhi-src were you able to get E2E tests working on M1?

https://github.com/sourcegraph/sourcegraph/pull/28783 brings in Puppeteer 12, which works on an M1. Once that's merged, we need to update these docs.