Create initial GETTING_STARTED.md

This is the very first draft

docs/GETTING_STARTED.md

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+# Getting Started
+
+## Linux
+- Clone the repository.
+- Install Rust using [rustup](https://rustup.rs).
+- Open the project folder in [Visual Studio Code](https://code.visualstudio.com).
+
+At this point, there are two options to open a new tunnel.
+
+### Method 1: Run & Debug
+- Install the [CodeLLDB](https://marketplace.visualstudio.com/items?itemName=vadimcn.vscode-lldb) VS Code extension.
+- In VS Code, press F5 to run & debug Burrow.\
+This flow does not work yet (panics).
+
+### Method 2: Cargo
+- In VS Code, press Ctrl+\` to open the terminal.
+- Type `cargo run`. 
+- Burrow should open a new tunnel (`Ok("tun0")`), then exit.
+
+## macOS
+
+## Windows