README: Update support policy

[danielchalmers]

Description

• States an end date for v6 support
• Adds v8
• Cleans up prerequisite notices

How Has This Been Tested?

Type 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 not work as expected)
• Documentation (fix or improvement to the website or code docs)

BEFORE

AFTER

Checklist

• The PR is submitted to the correct branch (dev).
• My code follows the code style of this project.
• I've added relevant tests.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[henon]

Thanks Daniel