Update Avatar Dialog Documentation to Describe How to Use Avatar Images

[BHSDuncan]

Update the docs to indicate the following:

• Escoria -> Dialog Simple -> Avatars Path contains the path of the folder that contains the dialog avatars for display.
• Avatars must be saved resource files (e.g. a saved AnimatedSprite) with the usual Godot .tres extension. The name of the file itself should be the same as the speaker's global_id, e.g. a character with global_id player would use player.tres as its avatar file.

[balloonpopper]

@BHSDuncan This is already done. https://docs.escoria-framework.org/en/devel/advanced/faq.html#how-do-i-create-an-avatar-to-use-in-conversations Yell if you think something's still missing.

[BHSDuncan]

@balloonpopper you're right it mostly is! Although I can't seem to see if we explicitly call out that the saved resource file has to use the .tres extension.

I see:

Click the down arrow next to the AnimatedTexture Texture property and choose save from the list. Save the file to the avatar location selected earlier. *The file name needs to match the global ID of the character the avatar is for!*

...so maybe the above can be edited to call out the .tres bit? Other than that, you're right: Everything else has been done from this ticket!