vim:plugs: Add NrrwRgn (narrow region)

> This plugin is inspired by the Narrowing feature of Emacs and means to
> focus on a selected region while making the rest inaccessible. You
> simply select the region, call :NR and the selected part will open in
> a new split window while the rest of the buffer will be protected.
> Once you are finished, simply write the narrowed window (:w) and all
> the changes will be moved back to the original buffer.

I want this to be able to diff two portions of a file without the need
of creating temporary files. (And the ability to automatically bring
back changes sounds nice too.)

Link: https://github.com/chrisbra/NrrwRgn

.local/share/vim/pack/plugins/start/NrrwRgn

@@ -0,0 +1 @@
+../opt/NrrwRgn