[ci skip] docs: make the syntax for generics easy to look up (#13754)

doc/tut2.rst

@@ -469,7 +469,8 @@ Generics
 ========
 
 Generics are Nim's means to parametrize procs, iterators or types
-with `type parameters`:idx:. They are most useful for efficient type safe
+with `type parameters`:idx:. Generic parameters are written within square
+brackets, for example ``Foo[T]``. They are most useful for efficient type safe
 containers:
 
 .. code-block:: nim