Flow Scenario wiki + update scenario help-menu

[marc-vdm]

The in-ui help menu for scenarios had a broken link so in fixing it I moved the info to the correct wiki and now link to the wiki instead of images.

Checklist

• Keep pull requests small so they can be easily reviewed.
• Update the documentation
  • For in-code documentation, please follow the numpy style guide.
  • For user documentation, please update the wiki in
    ./activity_browser/docs/wiki
• Update tests.
• Link this PR to related issues by using closing keywords.

If you have write access (otherwise a maintainer will do this for you):

• Categorize the PR by setting a good title and adding one of the labels:
  bug, feature, ui, change, documentation, breaking, ci
  as they show up in the changelog.
• Add a milestone to the PR (and related issues, if any) for the intended release.
• Request a review from another developer.

[coveralls]

coverage: 54.153% (-0.03%) from 54.185%
when pulling 1fa09f8 on marc-vdm:scenario-wiki-page
into 023eb5a on LCA-ActivityBrowser:main.