Suggestions for welcome.py script

[mwcraig]

I really like the welcome.py script! A couple of minor suggestions for it:

1. Add a prompt that you need to close the matplotlib window for the script to complete.
2. The numba warning ends with a line that starts "Install numba as described at the following webpage..." but there is no following web page.

[Jammy2211]

The welcome.py message has been updated:

https://github.com/Jammy2211/autocti_workspace/blob/main/welcome.py

    NOTE: If a matplotlib figure window appears, you may need to close it via the X button and then press 
    enter to continue the script.

I have updated the exception on numba to point to this webpage: https://pyautolens.readthedocs.io/en/latest/installation/numba.html

Thank you!