Improve README: Add Windows setup instructions

[EhsanEmamian]

The README currently only shows how to activate the virtual environment using a Unix-style command:

source supabase-py/bin/activate

This does not work on Windows (PowerShell or CMD), which can be confusing for developers trying to set up the project.

It would be helpful to add Windows-specific instructions, such as:

For PowerShell:
.venv\Scripts\activate

For Command Prompt (CMD):
.venv\Scripts\activate.bat

Adding these instructions would make the setup process clearer and more accessible for Windows users.

[waltterir]

Hi! I'd like to work on this issue.

[silentworks]

The instructions in the README.md is purely for developers looking to contribute to this project. We recommend WSL if you are on Windows OS as Make is a requirement for testing and is not available in Powershell or CMD. If you are looking to install the library into your existing project then use uv add supabase or pip install supabase as instructed in the README.md for the supabase package.