Fix README links to use main branch

[pavan-sh]

Summary

The README still referenced the next branch for the CI badge and contributing docs link, but the next branch no longer exists upstream.
This updates those URLs to point to main so the badge and contributing docs link work correctly.

Test plan

N/A, docs only change

[coderabbitai]

Walkthrough

The README.md file was updated to change branch references from "next" to "main" in two locations. The CI build status badge URL was modified to point to the main branch instead of the next branch. Additionally, the Contributing documentation link was updated to reference the main branch path instead of the next branch. These changes update the documentation to reference the main branch for both the CI build status and contributing guidelines.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: updating README links from the next branch to the main branch.
Description check	✅ Passed	The description clearly explains why the change was made and what was changed, providing relevant context about the deprecated next branch.

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