nvim: Add prose headline highlighting

Added simple highlighting plugin for prose headlines (and code
snippets). Will highlight the whole line a little from the
background and provide more space around it so it stands out.

Currently works (afaik) for markdown, rmd, norg filetypes.

nvim/.config/nvim/lua/plugins/prose.lua

@@ -22,6 +22,13 @@ return {
 			})
 		end,
 	},
+	-- displays prettier headlines mimicking the ones in emacs orgmode
+	{
+		"lukas-reineke/headlines.nvim",
+		dependencies = "nvim-treesitter/nvim-treesitter",
+	    config = true,
+	    ft = writing_ft,
+	},
 	-- generate an auto-updating html preview for md files
 	{
 		"iamcco/markdown-preview.nvim",