Document DynamicFont limitations and a possible workaround

This closes #30014.

doc/classes/DynamicFont.xml

@@ -12,6 +12,7 @@
 		dynamic_font.size = 64
 		$"Label".set("custom_fonts/font", dynamic_font)
 		[/codeblock]
+		[b]Note:[/b] DynamicFont doesn't support features such as right-to-left typesetting, ligatures, text shaping, variable fonts and optional font features yet. If you wish to "bake" an optional font feature into a TTF font file, you can use [url=https://fontforge.org/]FontForge[/url] to do so. In FontForge, use [b]File > Generate Fonts[/b], click [b]Options[/b], choose the desired features then generate the font.
 	</description>
 	<tutorials>
 	</tutorials>