Add neovim config with kickstart-modular. Update shell configs.

config/nvim/lua/custom/plugins/init.lua

@@ -0,0 +1,5 @@
+-- You can add your own plugins here or in other files in this directory!
+--  I promise not to create any merge conflicts in this directory :)
+--
+-- See the kickstart.nvim README for more information
+return {}