Update README with GitHub Actions permissions

[koppor]

I refined the starting example based on the most recent security things.

If one misses contents: write, one gets

❌ Resource not accessible by integration - https://docs.github.com/rest/pulls/pulls#create-a-pull-request

(https://github.com/koppor/openj9-hash-issue/actions/runs/18925607175)

If one misses "pull-request: write", one gets

Error: ❌ Validation Failed: {"resource":"PullRequest","field":"head","code":"invalid"} - https://docs.github.com/rest/pulls/pulls#create-a-pull-request

(https://github.com/koppor/openj9-hash-issue/actions/runs/18950395801/job/54113217034)

If one misses to change the settings in the repository, one gets

❌ GitHub Actions is not permitted to create or approve pull requests. - https://docs.github.com/rest/pulls/pulls#create-a-pull-request

With this update, it should be easy for users to copy and paste the basic configuration without having the need to create and maintain a separate token.

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[codecov-commenter]

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Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :warning: Please upload report for BASE (main@c3c7067). Learn more about missing BASE report. :exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #983   +/-   ##
=======================================
  Coverage        ?   84.92%           
=======================================
  Files           ?       16           
  Lines           ?      597           
  Branches        ?       85           
=======================================
  Hits            ?      507           
  Misses          ?       90           
  Partials        ?        0           

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