docs: correct vim.pack install instructions (#993)

Author: pji2918

README.md

@@ -55,7 +55,7 @@ This port of <a href="https://github.com/catppuccin/">Catppuccin</a> is special
 with Neovim 0.12's `vim.pack`
 
 ```lua
-vim.pack.add({ src = "https://github.com/catppuccin/nvim", name = "catppuccin" })
+vim.pack.add { { src = "https://github.com/catppuccin/nvim", name = "catppuccin" } }
 ```
 
 [lazy.nvim](https://github.com/folke/lazy.nvim)

doc/catppuccin.txt

@@ -27,7 +27,7 @@ INSTALLATION                                         *catppuccin-installation*
 with Neovim 0.12’s `vim.pack`
 
 >lua
-    vim.pack.add({ src = "https://github.com/catppuccin/nvim", name = "catppuccin" })
+    vim.pack.add { { src = "https://github.com/catppuccin/nvim", name = "catppuccin" } }
 <
 
 lazy.nvim <https://github.com/folke/lazy.nvim>