Fix broken note admonitions

[klamike]

Checklist

• [N/A] Appropriate tests were added
• [N/A] Any code changes were done in a way that does not break public API
• [N/A] All documentation related to code changes were updated
• [N/A] The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• [N/A] Any new documentation only uses public API

Additional context

This PR only modifies documentation formatting, fixing note admonition format on the getting started page. Currently live version:

[klamike]

With this PR:

[ChrisRackauckas]

Thanks! Simple but definitely something I had missed.