reduce arrows

if there's some course that's directly a prereq for a ton of others, make a box (likely via https://mermaid-js.github.io/mermaid/#/flowchart?id=subgraphs ) around all them and then have a single arrow to express the prereq

Start by inspecting the repository's current course chart and the linked Mermaid flowchart subgraphs documentation. Identify courses that are direct prerequisites for many others, then group those courses visually with a single prerequisite arrow; done means the chart is less cluttered while preserving the prerequisite relationships.

Scritto dal modello di indicizzazione a partire dal testo della issue.