Improvements tracking issue

• Better curate the contents in the section on Linux and raise the bar by removing material that is too introductory
• Add section on documentation and technical writing.
• Add an exercise in the section on documentation on making mermaid diagrams, with a short problem description involving a system architecture, database model, and/or sequence diagram.
• Add better docker tutorials, projects and references
• Improve and expand the rust material
• Elaborate on testing, tdd
• Add material on functional programming
• Add material on observability
• Add material on machine learning
• Add resources for gamedev
• Add material on bitcoin
• Add material on language engineering
• Pick and choose from https://github.com/facundoolano/software-papers

Start with the unchecked checklist in issue #136 and review the corresponding sections of the learning path. Break the broad tracking issue into focused tasks, then define completion separately for each requested topic and resource update; no specific files or tests are named.