Link the Random number generation tutorial in the class reference

(cherry picked from commit 802c1e4df1975ff6ed11eacefe7e12d40b295b32)

doc/classes/RandomNumberGenerator.xml

@@ -15,6 +15,7 @@
 		[/codeblock]
 	</description>
 	<tutorials>
+		<link title="Random number generation">https://docs.godotengine.org/en/latest/tutorials/math/random_number_generation.html</link>
 	</tutorials>
 	<methods>
 		<method name="randf">

modules/gdscript/doc_classes/@GDScript.xml

@@ -7,6 +7,7 @@
 		List of core built-in GDScript functions. Math functions and other utilities. Everything else is provided by objects. (Keywords: builtin, built in, global functions.)
 	</description>
 	<tutorials>
+		<link title="Random number generation">https://docs.godotengine.org/en/latest/tutorials/math/random_number_generation.html</link>
 	</tutorials>
 	<methods>
 		<method name="Color8">