Remapped shift-tab to tab leftwards in insert mode.

[samjwill]

Many programs (Notepad++, Microsoft Word, Sublime Text, GNU nano, VS Code, etc.) map shift-tab to an inverse tab. Vim, by default, does not map this to anything, and when the combination is pressed, a regular tab character is inserted.

I think it might be a good tweak to add this mapping if Shift-Tab in insert mode is not mapped to anything else :)