Update README instructions for the right Python version

[dr-smgad]

Provide environment information

The installation instructions in the README file are not accurate as the conda env creation step mentions python=3 while this won't work (at least on Windows OS as I tried, it gives error can't find labelme command, also I tried to add to Path but in vain), when changing this to python=3.8 everything worked fine.

What OS are you using?

Windows

Describe the Bug

Anaconda command prompt can't find command "labelme" after activating the labelme conda environment.

Expected Behavior

No response

To Reproduce

No response

[wkentaro]

I can run with Python 3.9 and 3.10 on Conda on macOS. So could you check again with the latest labelme?