doc: add 2.x and 3.x to PLATFORM_SUPPORT.md

[BBosman]

Description

Update PLATFORM_SUPPORT.md to mention the supported cordova and platform versions for the 2.x and 3.x versions of the plugin.

The mentioned versions are based on the information in the <engines> tag in plugin.xml for versions 2.3.0 and 3.0.0.

Related Issue

n/a, just a minor docs change.

Motivation and Context

The previous information was out of date.

How Has This Been Tested?

n/a, just a docs change

Screenshots (if appropriate):

n/a

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:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.