Use 4-space indent for nested unordered list to make it render correctly with MkDocs

[bact]

Option 1/3 to fix #916

Options:

• Use 4-space indent for nested unordered list to make it render correctly with MkDocs #920
• Use one-level unordered list to avoid formatting issue with MkDocs #921
• Collapse a nested list to a single-level list to avoid rendering issue in MkDocs #922

Only one of the three should be used

[goneall]

Closing this PR since the alternative was accepted and merged.

Thanks @bact for providing the choices!