docs(app): clarify iOS setup instructions, especially around use_frameworks

[gosunman]

Description

• I fixed the frequently asked issue ([🐛] Build fails on macOS M1 with sample React Native 0.71.1 project #6853) after looking https://github.com/mikehardy/rnfbdemo/blob/main/make-demo.sh by @mikehardy
• according to make-demo.sh, I updated the documentation (iOS setup part in getting started)

Related issues

#6853

Release Summary

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
  • Yes
  • No (link should be changed with ../blob/main/CONTRIBUTING.md instead of ../CONTRIBUTING.md)
• My change supports the following platforms;
  • Android
  • iOS
• My change includes tests;
  • N/A
  • e2e tests added or updated in packages/\*\*/e2e
  • jest tests added or updated in packages/\*\*/__tests__
• (N/A) I have updated TypeScript types that are affected by my change.
• This is a breaking change;
  • Yes
  • No

Test Plan

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[mikehardy]

Quite a few thoughts on this one - i think a couple of the suggested changes could be really helpful, but many of the suggestions here are not valid for react-native-firebase specific install docs I don't think

What do you think?

[gosunman]

@mikehardy

I reviewed the comments you gave me one by one.
As a result, there are only a few lines left. lol
As you've already left a lot of comments on "Issues",
There was no fault in the document. Haha

My PR is a modification to the extent that it once again clarifies where the code should go in,
but thank you for your detailed review.

I can understand if you accept this PR or reject it.

Anyway, thank you again for the detailed review. :)

[jckw]

Would just like to add that I was recently tripped up by exactly this. I worked out that I needed to make those changes, but I would've saved a few hours had the docs read like this.

🎉

[mikehardy]

Apologies this went to sleep! I think it is small now but still quite a useful change, thank you!