docs(ios): update upgrade guidelines of iOS

[wwwcg]

Before submitting a new pull request, please make sure:

• Test cases have been added/updated/passed for the code you will submit.
• Documentation has added or updated.
• Commit message is following the Convention Commit guideline with maximum 72 characters.
• Squash the repeat code commits, short patches are welcome.

[hippy-service]

Hi, @wwwcg. Thanks for your PR! 👏

🏷️ You can leave a comment in this PR with #help tag when you need help (e.g. some status checks run failed due to internal issue), admin team members will help asap.

[hippy-service]

🎉 It seems that this pull request has been approved by all required reviewers. As it only contains one normal commit, I will rebase and merge it automatically via add action(rebase-merge) label.

• SHA: 66c60d3