updated readme

[ayo-klaytn]

Proposed changes

Updates ReadME file. Removed the "change the master branch to main" section

Types of changes

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• Bugfix
• New feature or enhancement
• Others

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• I have read the CONTRIBUTING GUIDELINES doc
• I have signed the CLA
• Lint and unit tests pass locally with my changes ($ make test)
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

Related issues

• Please leave the issue numbers or links related to this PR here.

Further comments

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[CLAassistant]

All committers have signed the CLA.