nvim: enabled ghost_text in nvim-cmp

I finally found out how to do this!

.config/nvim/lua/blake/lsp.lua

@@ -185,6 +185,9 @@ M.cmp = function()
             return vim_item
          end,
       },
+      experimental = {
+         ghost_text = true,
+      }
    }
 end -- <<<