feat: make nvim-web-devicons an optional dependency (#328)

* chore: make `web-devicons` optional

* docs: update readme install instructions

README.md

@@ -27,12 +27,13 @@ Install `avante.nvim` using [lazy.nvim](https://github.com/folke/lazy.nvim):
     -- add any opts here
   },
   dependencies = {
-    "nvim-tree/nvim-web-devicons", -- or echasnovski/mini.icons
     "stevearc/dressing.nvim",
     "nvim-lua/plenary.nvim",
     "MunifTanjim/nui.nvim",
-    --- The below is optional, make sure to setup it properly if you have lazy=true
+    --- The below dependencies are optional,
+    "nvim-tree/nvim-web-devicons", -- or echasnovski/mini.icons
     {
+      -- Make sure to setup it properly if you have lazy=true
       'MeanderingProgrammer/render-markdown.nvim',
       opts = {
         file_types = { "markdown", "Avante" },