[DOCS] Add Windows/WSL onboarding to Getting Started Page

### Describe the issue

Windows users are currently left in the dark when it comes to setting up PDK using WSL. The Getting Started guide should be updated to have a specific WSL onboarding section.

### Links

https://aws.github.io/aws-pdk/getting_started/index.html

Start with the linked Getting Started guide at https://aws.github.io/aws-pdk/getting_started/index.html and inspect how the current setup instructions are organized. Add a dedicated Windows/WSL onboarding section that explains setting up PDK with WSL, then verify that the published guide clearly covers the requested setup path.

Written by the indexing model from the issue text.