Update README.md build badge

[bjfish25]

Proposed changes

Fixes Readme description showing no build badge for master branch.

Issues for these changes

No issues created. But issue seen here: https://github.com/optum/cloudig/workflows/build/badge.svg?branch=main

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (changes to code, which do not change application behavior)

Checklist

• I have filled out this PR template
• I have read the CONTRIBUTING doc
• I have added automated tests that prove my fix is effective or that my feature works
• I have added necessary documentation (README.md, CHANGELOG.md, etc. - if appropriate)

Dependencies and Blockers

Relevant Links

Further comments

[CLAassistant]

All committers have signed the CLA.