Add documentation about defining custom portraits (#819)

Author: bitbrain

addons/dialogic/Documentation/Content/FAQ/custom-portraits.md

@@ -0,0 +1,3 @@
+# Custom portraits
+
+You can define custom portraits that are animated or have particle effects and shaders by selecting a path to a scene (*.tscn) rather than to an image in the character screen. Your custom scene can be a Control node, a sprite or an animated sprite. When selecting a Node2D Dialogic might be unable to access its intended dimensions due to the nature of Node2D not having a specific size attribute defined.

addons/dialogic/Documentation/Content/FAQ/Portraits.md renamed to addons/dialogic/Documentation/Content/FAQ/portraits-not-showing.md

@@ -25,7 +25,8 @@ This project is made possible by the support of our [Patreons](https://www.patre
 - [Can I use C# with Dialogic?](./FAQ/CSharp.md)
 - [How can I make a dialog show up in game?](./FAQ/how-to-make-dialog-show-up-in-game.md)
 - [The plugin is cool! Why is it not shipped with Godot?](./FAQ/plugin-shipped-godot.md)
-- [Portraits not showing in game?](./FAQ/Portraits.md)
+- [Portraits not showing in game?](./FAQ/portraits-not-showing.md)
+- [How can I define animated portraits?](./FAQ/custom-portraits.md)
 - [My resolution is too small and the dialog is too big.](./FAQ/resolution-small-dialog-big.md)
 - [Using signals?](./FAQ/Signals.md)
 - [Why are you not using graph nodes?](./FAQ/why-not-graph-nodes.md)