docs: add a runnable QEMU usage example

[rinadavidyuk826-sudo]

Fixes #95

Summary

• add a runnable workflow example that uses QEMU to run an arm64 container on a GitHub-hosted runner
• explain that the action registers user-mode emulators with binfmt_misc for later workflow steps
• clarify that the action does not install qemu-system tools or add qemu-* binaries to PATH

Verification

• reviewed the README rendering and command example for correctness