Update readme to add pyinstaller option

[Androidbeingx]

This PR updates the README to document Option 4: Standalone binary (PyInstaller) for execution-metrics-collector.

Changes

• Added a new PyInstaller standalone binary installation option.
• Documented how to use a pre-built binary from GitHub Container Registry.
• Added instructions for building the binary from source using a manylinux_2_28 container.
• Added explanations about glibc compatibility and how to check it before deploying the binary.
• Added troubleshooting guidance for common PyInstaller/glibc/SSL issues.
• Added a complete HPC workflow example, covering binary building, deployment, metrics collection, and local analysis.
• Updated the installation options and constraints-file references in the README.
• Clarified that the standalone binary is primarily intended for running execution-metrics-collector on systems where Python, pip, or a container runtime cannot be installed.

Motivation
The new option makes it possible to run execution-metrics-collector on HPC compute nodes or other restricted environments without requiring a Python installation or container runtime.

[jmfernandez]

Thanks for the contribution!! I'm going to merge it right now.

I have a question, can these steps be replicated/extrapolated using singularity instead of docker?

[Androidbeingx]

Good catch!
I am gonna do test to try it. And update the docs if success.