Fix link to Docutils' `.. class::` directive (#14193)

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>

doc/usage/restructuredtext/basics.rst

@@ -402,7 +402,8 @@ Docutils supports the following directives:
 
     .. _rstclass:
 
-  - :dudir:`class` (assign a class attribute to the next element)
+  - :dudir:`class <setting-class-attributes>`
+    (assign a class attribute to the next element)
 
     .. note::