Update README.md

[marksou]

TT-6598 Update MongoDB supported versions link. Changed Operator docs link to the new docs version rather than the GH version. Minor editing.

Description

Updated Broken link to supported MongoDB versions

Related Issue

Motivation and Context

Prevents a 404 error on current link

Test Coverage For This Change

Screenshots (if appropriate)

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

• Make sure you are requesting to pull a topic/feature/bugfix branch (right side). If PRing from your fork, don't come from your master!
• Make sure you are making a pull request against our master branch (left side). Also, it would be best if you started your change off our latest master.
• [x ] 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.

[buraksekili]

Thanks @marksou