Minor refactor of Outcome and Overview documentation

[ahouseholder]

• Fix outcomes doc
• Small refactor of overview section
• apply black formatter to python and markdownlint to markdown
• fix a few broken links (side effects of other changes)

Copilot summary

This pull request makes several improvements and corrections to the SSVC documentation, focusing on navigation, organization, and clarity. The most significant changes include reorganizing documentation sections for better usability, adding a new resource page, and clarifying references to outcomes and decision points. Additionally, some minor formatting and content updates were made to improve readability.

Documentation organization and navigation:

• The "SSVC Overview" section and its links have been moved from the root to the tutorials/ directory for consistency and improved navigation. All references in docs/index.md have been updated accordingly.
• The file docs/ssvc_overview.md was renamed to docs/tutorials/ssvc_overview.md, and internal PDF embed links were updated to reflect the new location. [1] [2]

New and improved resource content:

• Added a new "Other Resources" page at docs/tutorials/other_resources.md, providing curated links to videos, articles, and external SSVC content.

Clarification and correction of outcomes documentation:

• Created a new docs/reference/decision_points/outcomes.md to document outcome decision points, replacing the old docs/reference/code/outcomes.md file and updating all references accordingly. [1] [2] [3] [4]

Minor improvements and formatting:

• Cleaned up whitespace, improved list formatting, and clarified rationale and alternatives in the versioning ADR. [1] [2] [3]
• Updated the code documentation index to include and clarify references to new and deprecated modules.
• Removed extraneous blank lines and improved formatting in several documentation files for consistency. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

These changes collectively improve the structure, clarity, and discoverability of the SSVC documentation.

[ahouseholder]

Merging in the interest of getting #958 across the line.