docc: readme.md

[choman]

Describe your issue

Readme should mention the supported versions of task warrior. 2, 3, or both

Steps to reproduce

No steps as this is a document update

What was the expected result?

No result other than correct decision making

Put here any screenshots or videos (optional)

No response

How can we contact you (optional)

No response

Would you like to work on this issue?

None

By submitting this issue, I have confirmed that:

• I have starred the repo ⭐ and watched 👀 it on GitHub and followed the contribution guidelines.