Clarify which Python versions are supported

[rootulp]

Context

staking-deposit-cli/README.md

Lines 199 to 205 in fdab65d

	##### Step 0. Python version checking
	Ensure you are using Python version >= Python3.8:
	```sh
	python3 -V
	```

Problem

The README states Python > 3.8 is supported but that's not the case. See #363

Proposal

Until #363 is resolved, can the README explicitly state the versions of Python that are supported

[yorickdowne]

Come on over, we have Python 3.11, 3.12 and even 3.13.0-rc.1 in our CI. But minimum 3.9, we dropped 3.8.

Recommend sticking to Holesky with our fork until we have the re-audit done. And, we can use all the help we can get in testing.

https://github.com/eth-educators/ethstaker-deposit-cli