Docs: Add Windows WSL build instructions

[Ritish017]

This PR adds documentation for building CCExtractor on Windows using WSL (Ubuntu).

The guide includes:

• WSL and Ubuntu setup
• Rust installation
• Required dependencies (libclang, tesseract, gpac)
• Build steps
• Common build errors and fixes

This should help first-time contributors build CCExtractor more easily on Windows.

[Ritish017]

Hi 👋
This guide is based on a fresh Windows + WSL setup.
Happy to update or adjust anything if needed.
Thanks for reviewing!

[cfsmp3]

Thank you for this helpful documentation! WSL build instructions will be useful for Windows users.

However, please fix the README link placement. Currently it's inserted between "Downloads" and "Usage", which breaks the flow:

Downloads for precompiled binaries...
- [Building on Windows using WSL](docs/build-wsl.md)   <-- interrupts flow
Extracting subtitles is relatively simple...

Please either:

1. Create a "Building from Source" section in the README and place the link there, or
2. Move the link to the end of the "Installation and Usage" section

The documentation content itself is good - just needs this structural fix.

[Ritish017]

Thanks for the review!

I’ve moved the WSL build link into a dedicated “Building from Source” subsection,
placed just before the “Compiling CCExtractor” section, as suggested.

Please let me know if this placement works.