Add example of loading a font from .ttf file

As this is a multi-step process it would be nice to have this documented.

doc/classes/DynamicFont.xml

@@ -5,6 +5,12 @@
 	</brief_description>
 	<description>
 		DynamicFont renders vector font files (such as TTF or OTF) dynamically at runtime instead of using a prerendered texture atlas like [BitmapFont]. This trades the faster loading time of [BitmapFont]s for the ability to change font parameters like size and spacing during runtime. [DynamicFontData] is used for referencing the font file paths.
+		[codeblock]
+		var dynamic_font = DynamicFont.new()
+		dynamic_font.font_data = load("res://BarlowCondensed-Bold.ttf")
+		dynamic_font.size = 64
+		$"Label".set("custom_fonts/font", dynamic_font)
+		[/codeblock]
 	</description>
 	<tutorials>
 	</tutorials>