Docs for some nodes in visual shader

Fix typo in `VisualShaderNodeCompare.ComparisonType` name.

doc/classes/VisualShaderNodeColorConstant.xml

@@ -1,8 +1,11 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <class name="VisualShaderNodeColorConstant" inherits="VisualShaderNode" category="Core" version="3.2">
 	<brief_description>
+		A [Color] constant to be used within the visual shader graph.
 	</brief_description>
 	<description>
+		Has two output ports representing RGB and alpha channels of [Color].
+		Translated to [code]vec3 rgb[/code] and [code]float alpha[/code] in the shader language.
 	</description>
 	<tutorials>
 	</tutorials>
@@ -10,6 +13,7 @@
 	</methods>
 	<members>
 		<member name="constant" type="Color" setter="set_constant" getter="get_constant" default="Color( 1, 1, 1, 1 )">
+			A [Color] constant which represents a state of this node.
 		</member>
 	</members>
 	<constants>