Add release badge to README

[jacobsalway]

Purpose of this PR

• Add a release badge to the README
• Remove codecov.yaml since this isn't being run as part of CI

Change Category

Indicate the type of change by marking the applicable boxes:

• Bugfix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that could affect existing functionality)
• Documentation update

Checklist

Before submitting your PR, please review the following:

• I have conducted a self-review of my own code.
• I have updated documentation accordingly.
• I have added tests that prove my changes are effective or that my feature works.
• Existing unit tests pass locally with my changes.

[jacobsalway]

/assign @ChenYi015 @ImpSy

[ChenYi015]

/lgtm

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ChenYi015

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [ChenYi015]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment