Clarify czkawka_gui installation steps on macOS

[yrue]

Hi! First of all, thank you for this awesome project 🙌 I'm trying to set up czkawka_gui on macOS and I wanted to ask for clarification about the setup steps and propose an improvement to the docs and CLI flow.

🔍 Steps I followed

1. Installed with:

   brew install czkawka

   (from the README: [macOS section](https://github.com/qarmin/czkawka/blob/master/czkawka_gui/README.md#mac))

2. Then followed the compilation instructions from the README:

   /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
   brew install rustup gtk4 adwaita-icon-theme ffmpeg librsvg libheif libraw pkg-config
   rustup-init
   cargo run --release --bin czkawka_gui

3. Restarted the terminal, then ran:

   cargo run --release --bin czkawka_gui

4. Got the error:

   error: could not find `Cargo.toml` in `<path>` or any parent directory
   

5. Realized I hadn’t cloned the source repo yet — once I did:

   git clone https://github.com/qarmin/czkawka.git
   cd czkawka
   cargo run --release --bin czkawka_gui

   — it worked as expected 🎉

---

❓ Questions

• Could we clarify in the docs that compiling with Cargo requires cloning the repo first? The current flow might confuse users coming from the brew install czkawka step who don't realize they need the source code locally.
• What’s the relationship between the Homebrew-installed czkawka and compiling from source? Should users do either install OR compile, not both?
• Would it make sense to:
  • Mention in the README that cargo run assumes you're inside the repo with Cargo.toml?
  • Add a helpful hint when the Cargo.toml file is not found (if possible) that suggests cloning the repo?