Add End of Life text to README

[edthedev]

Context

This product is open source and so much comply with our checklist. Our usual end-of-life language.

Tasks

• [ ] calculate end-of-life for known components: supported Python versions, SOAR API. An educated guess may be required for SOAR API.
• [ ] add the end-of-life information to README.md per https://answers.uillinois.edu/illinois/109544