Add maintenance mode notice to README

[Mike-Hermans]

Added maintenance mode notice and alternatives.

Issue link

Description

Add maintenance mode notice to the readme file, as this project no longer receives active development.

How Has This Been Tested?

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 not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.