[Feature request] Ability to set margin along edges

[alejandro5042]

Is your feature request related to a problem? Please describe.
When writing long markdown files, would be nice if I could set a margin on the text, so that lines aren't super long on screen.

Describe the solution you'd like
An editor setting to set the left and right margin, perhaps as a percentage of the window size.

Describe alternatives you've considered
A focus mode button -- maybe you can use this to enable the margin or not. Or perhaps not do this because its feature creep... but figured asking doesn't hurt ;) Would fit well with the type of app this is though.

Additional context
N/A