Add Python 3.9 requirement and WSL note to setup docs

[NihalShinde4933]

Summary

This PR updates docs/getting_started.rst to:

• Clarify that Python 3.9 is required for development.
• Recommend using WSL instead of native Windows for Kolibri development.

Motivation

During setup, I encountered issues due to:

• pre-commit needing Python 3.9+ (not mentioned explicitly).

• Running Kolibri directly on Windows (unsupported as per maintainers).

This documentation improvement aims to save new contributors from similar issues.

Related Issue

Closes https://github.com/learningequality/kolibri/issues/13458

Notes

• Fixed CRLF to LF line endings to avoid whole-file diffs.
• Re-submission after feedback on previous PR.

Screenshots / Changes

[github-actions[bot]]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.19.0a0.dev0_git.73.g0bb4709f.pex
Windows Installer (EXE)	kolibri-0.19.0a0.dev0+git.73.g0bb4709f-windows-setup-unsigned.exe
Debian Package	kolibri_0.19.0a0.dev0+git.73.g0bb4709f-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.19.0a0.dev0+git.73.g0bb4709f.dmg
Android Package (APK)	kolibri-0.19.0a0.dev0+git.73.g0bb4709f-0.1.4-debug.apk
Raspberry Pi Image	kolibri-pi-image-0.19.0a0.dev0+git.73.g0bb4709f.zip
TAR file	kolibri-0.19.0a0.dev0+git.73.g0bb4709f.tar.gz
WHL file	kolibri-0.19.0a0.dev0+git.73.g0bb4709f-py2.py3-none-any.whl

[MisRob]

Hi @NihalShinde4933, do you plan to address feedback?