[Feature request] Hope we can have an outline(or TOC)

[naive231]

Is your feature request related to a problem? Please describe.
In a long note, we may have a structured content inside.
Sometimes we can't clearly or remember where we are in this note.

Describe the solution you'd like
The most convenient and concise way is an outline, or TOC(Table Of Content) like this:

Describe alternatives you've considered
Nope.

Additional context
If we have a highlighted bar indicated which paragraph we are located, that would be a great plus.