Fix typo and missing description of content in folder

[mingxin-zheng]

Fixes #2001 .

Description

These fixes are suggested by Cursor + claude-4-sonnet, with a prompt:

Please review the documentation (markdown/jupyter) in the tutorial repo  for clarity, with a focus of typo fixes and language refinement

Checks

• Avoid including large-size files in the PR.
• Clean up long text outputs from code cells in the notebook.
• For security purposes, please check the contents and remove any sensitive info such as user names and private key.
• Ensure (1) hyperlinks and markdown anchors are working (2) use relative paths for tutorial repo files (3) put figure and graphs in the ./figure folder
• Notebook runs automatically ./runner.sh -t <path to .ipynb file>

[Copilot]

Pull Request Overview

This PR cleans up typos and refines the README documentation across several tutorial folders, and adds a missing overview section for the 3D regression tutorial.

• Standardizes phrasing (e.g., "In summary," capitalization, spelling corrections).
• Improves clarity by adding a Tutorial Overview and run instructions in the 3D regression README.
• Fixes minor spelling errors and redundant wording in existing READMEs.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
vista_3d/README.md	Lowercased "In summary," and added "a" before model.
vista_2d/README.md	Lowercased "In summary,".
pathology/tumor_detection/README.MD	Corrected "compare to" → "compared to".
nnunet/README.md	Removed redundant clause, fixed "diretory" spelling; improved "singlular" → "singular".
acceleration/distributed_training/distributed_training.md	Rephrased multi-node training example for consistency.
README.md	Fixed "dictionary-base" → "dictionary-based".
3d_regression/README.md	Added descriptive overview and run instructions with Colab badge.