Update Dialogs tutorial, explain how to use regular script syntax

[ivan-mogilko]

https://adventuregamestudio.github.io/ags-manual/acintro8.html

This came up on forums, the existing Tutorial on Dialog script has words like:

This is not the same type of script that we've used for our Events like picking up the key. It's a much simpler dialog-only scripting language

and does not mention that it in fact has full script capabilities, and how to use them.

UPD.

Also perhaps mention that the primary purpose of dialogs is to have branches in conversation. For a sequence of speech lines one could use Say commands in script too.

[ericoporto]

Made a small note here for now: https://github.com/adventuregamestudio/ags-manual/wiki/acintro8/_compare/9241b53%5E...9241b53