[Feature request] Option to enable preview by default

[emvaized]

Describe the solution you'd like
Would be great to have an option to always enable preview when file opened, if preview is available for this filetype. Probably it should be disabled by default in order to not confuse new users.

[iitzRichie]

Same. I was gonna suggest the same thing. Or have an option to have the preview as the main window. I want to see Markdown elements in real time, not have to manually enable the preview before I can see it.