[chore](doc) Improve README formatting for clarity

[xiedeyantu]

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

Thank you for your contribution to Apache Doris.
Don't know what should be done next? See How to process your PR.

Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[morrySnow]

run buildall

[morrySnow]

/review

[github-actions]

PR approved by at least one committer and no changes requested.

[github-actions]

PR approved by anyone and no changes requested.

[github-actions]

No blocking issues found. This PR is limited to README wording/formatting fixes, and the updated links/text remain consistent with the surrounding document.

Critical checkpoint conclusions:

• Goal and tests: The goal is documentation clarity; the diff accomplishes it. No runtime tests are needed for README-only wording changes.
• Scope: The modification is small, focused, and limited to the intended README section.
• Concurrency/lifecycle/config/compatibility: Not applicable; no code, config, storage format, protocol, or runtime lifecycle changes.
• Parallel paths: Not applicable for this documentation-only edit.
• Conditional checks/error handling/memory/data correctness/transactions: Not applicable.
• Test/result coverage: No generated test results are required for documentation-only changes.
• Observability/performance: Not applicable.

User focus points: No additional user-provided review focus was specified.