streamline event hub docs

[sjvans]

• [ ] rename guide to event-hub.md → would break links in event hub docs
• move content of Node.js guide to open source readme?
• ensure links to open source repos in both the general messaging guide as well as the stack specific content
  • check: link to the repos or link to the plugins entry that links to the repos?

[t-bonk]

LGTM

[github-actions]

Spelling Mistakes

• about/index.md:88:55 Unknown word "Appl"

Generally, for each spelling mistake there are 2 ways to fix it:

1. Fix the spelling mistake and commit it.
2. The word is incorrectly reported as misspelled → put the word on the project-words.txt list, located in the root project directory.