README enhancement for tslab install and --python option

[TonyGravagno]

Install instructions in README:

tslab install [--python=python3]
By default, tslab is registered with python3 in unix-like system and python in Windows. If Jupyter is installed with a different Python in your system, please specify the python command with --python flag.

I already have Python3 installed and the python.exe is version 3, so there isn't a need to specify the (yes, optional) python command.
This isn't clear in that instruction.
So, after checking python --version, it seems tslab install and no option did install correctly.

Suggested enhancement:

By default, tslab is registered with python3 in unix-like (Linux) systems and python in Windows. On a unix-like (Linux) system, if python3 --version returns a version, there is no need to specify a python version. On Windows, if python --version returns a version, there is no need to specify a python version. The python command may already be a synonym for Python v3. If Jupyter is installed with a different synonym/alias to execute Python in your system, specify the python command with --python flag.

[gnaaruag]

yup a simple tslab install as opposed to the tslab install [--python=python3] seems to do the trick. A bit confusing, a fix to that would be nice.