docs: Fix lua keybindings in README (folke#321)

The lua keybinds below were like this:

```
vim.keymap.set("n", "<leader>xl", function() require("trouble").open("quickfix") end)
vim.keymap.set("n", "<leader>xq", function() require("trouble").open("loclist") end)
```

As it might not be noticeable the `<leader>xl` keybinding was opening the `quickfix` and the `<leader>xq` keybinding was opening the `loclist`.

So I thought about changing the order just to be more straight forward to new users and to be in sync with the vim keybindings above the lua ones.

README.md

@@ -172,8 +172,8 @@ nnoremap gR <cmd>TroubleToggle lsp_references<cr>
 vim.keymap.set("n", "<leader>xx", function() require("trouble").open() end)
 vim.keymap.set("n", "<leader>xw", function() require("trouble").open("workspace_diagnostics") end)
 vim.keymap.set("n", "<leader>xd", function() require("trouble").open("document_diagnostics") end)
-vim.keymap.set("n", "<leader>xl", function() require("trouble").open("quickfix") end)
-vim.keymap.set("n", "<leader>xq", function() require("trouble").open("loclist") end)
+vim.keymap.set("n", "<leader>xq", function() require("trouble").open("quickfix") end)
+vim.keymap.set("n", "<leader>xl", function() require("trouble").open("loclist") end)
 vim.keymap.set("n", "gR", function() require("trouble").open("lsp_references") end)
 ```