Add mermaid package

[Eloitor]

📖 Description

wrapper for https://mermaid.js.org/ to draw diagrams on webview

📦 New package

• I have updated the packages/list.art:
  • All you have to do is add an entry like:

    packageName: "owner/repo"

• The repo in question is formatted as a valid Arturo package:
  • either have a main.art file and/or an info.art file specifying the entry point, depends and requires
• There is at least one published release:
  • Arturo's package manager versioning uses the published releases' tags which have to conform to SemVer

[drkameleon]

Ready to merge! 🚀