Consider avoiding gitlab-specific characters/symbols in markdown in favor of unicode symbols

Symbol short cuts like 🔹 (':small_blue_diamond:') render in markdown documents viewed on GitLab but not elsewhere, like vscode. A unicode character like "✓" conveys the same meaning and render equally well on GitLab, in vscode, and as raw text.

For example, see:

• https://code.usgs.gov/ghsc/nshmp/nshmp-haz/-/blob/5c3e843ecd1e5aaaabf6af500420ff6ef030aaae/docs/pages/Model-Editions.md#L29