Add nvim-tree setup

templates/nvim/lua/options.lua.j2

@@ -55,5 +55,9 @@ vim.o.background = 'light'
 vim.o.laststatus = 2
 vim.o.statusline = ' %F %m%r%w %= %{hostname()}   %{strlen(&ft)?&ft:"none"} %{(&bomb?",BOM":"")} %{&ff}  %l/%L  %c %P'
 
+-- use a dedicated file explorer
+vim.g.loaded_netrw = 1
+vim.g.loaded_netrwPlugin = 1
+
 -- python interpreter
 vim.g.python3_host_prog = './env/bin/python'