Update example for flat text buttons

[Ibrahim2750mi]

Documentation request:

What documentation needs to change?

The example for flat text buttons.

Where is it located?

https://github.com/pythonarcade/arcade/blob/development/arcade/examples/gui_flat_button.py

What is wrong with it? How can it be improved?

It would be good to show how to align the buttons at a desired coordinate. As there is no mention of it in the whole docs of flat text button.