docs: git clone concurrently

[breezewish]

What problem does this PR solve?

Issue Number: ref #4019

Problem Summary:

Polish the README to fetch submodule concurrently.

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• SchrodingerZhu
• fuzhe1989

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

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[breezewish]

/merge

[ti-chi-bot]

@breezewish: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

You only need to trigger /merge once, and if the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

If you have any questions about the PR merge process, please refer to pr process.

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: ba846bf

[sre-bot]

Coverage for changed files

no c/c++ source change detected

Coverage summary

Functions  MissedFunctions  Executed  Lines   MissedLines  Cover
18218      9785             46.29%    203973  97904        52.00%

full coverage report (for internal network access only)

[sre-bot]

Coverage for changed files

no c/c++ source change detected

Coverage summary

Functions  MissedFunctions  Executed  Lines   MissedLines  Cover
18218      9785             46.29%    203973  97905        52.00%

full coverage report (for internal network access only)

[ti-chi-bot]

@breezewish: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[sre-bot]

Coverage for changed files

no c/c++ source change detected

Coverage summary

Functions  MissedFunctions  Executed  Lines   MissedLines  Cover
18218      9786             46.28%    203973  97920        51.99%

full coverage report (for internal network access only)