vim:plugs: Add vim-sort-folds

> Sorting folds is not easily possible in vanilla vim. You could join
> all lines in a fold, sort and split them up again; however, it is time
> consuming and tedious.
>
> This little plugin solves that issue: It sorts a visually selected
> region while keeping closed folds intact. Since folds can be created
> in a variety of ways, it is therefore straight-forward to sort
> arbitrary groups of text based on their first line.

.gitmodules

@@ -71,6 +71,9 @@
 [submodule "vim-obsession"]
 	path = .config/vim/pack/plugins/opt/vim-obsession
 	url = https://github.com/tpope/vim-obsession
+[submodule "vim-sort-folds"]
+	path = .config/vim/pack/plugins/opt/vim-sort-folds
+	url = https://github.com/obreitwi/vim-sort-folds
 [submodule "vim-surround"]
 	path = .config/vim/pack/plugins/opt/vim-surround
 	url = https://github.com/tpope/vim-surround