Feat: Update readme for Helm Charts

[adriangonciarz]

Description

Readme under charts/selenium-grid/README.md is updated with the details of adding repo and installing directly from Helm repo instead of building from code

Motivation and Context

Helm Repo has been recently created in Github Pages so no longer it's needed to build chart from this repo

Types of changes

• Bug fix (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 change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[diemol]

Thank you, @adriangonciarz!