docs: script later is module too

[ZJvandeWeg]

Description

While it was clear in the documentation that loading the index.js needs a type="module" in the script tag, it didn't register to me the later version needed too. This change breaks JS highlighting, but would've saved me an hour. (I don't know JS, so maybe this PR isn't needed?)

Related Issue(s)

Checklist

• [ ] I have read the contribution guidelines
• [ ] Suitable unit/system level tests have been added and they pass
• [ ] Documentation has been updated
  • [ ] Upgrade instructions
  • [ ] Configuration details
  • [ ] Concepts
• [ ] Changes flowforge.yml?
  • [ ] Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • [ ] Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production

Labels

• [ ] Backport needed? -> add the backport label
• [ ] Includes a DB migration? -> add the area:migration label