[doc] Add link to Generic in typing (GH-22125)

[doc] Add link to Generic in typing (GH-22125) · python/cpython@5bfd60f

Original file line number	Diff line number	Diff line change
`@@ -818,7 +818,7 @@ These are not used in annotations. They are building blocks for creating generic`
`818`	`818`
`819`	`819`	`Type variables exist primarily for the benefit of static type`
`820`	`820`	`checkers. They serve as the parameters for generic types as well`
`821`		`- as for generic function definitions. See class Generic for more`
	`821`	+ as for generic function definitions. See :class:`Generic` for more
`822`	`822`	`information on generic types. Generic functions work as follows::`
`823`	`823`
`824`	`824`	`def repeat(x: T, n: int) -> Sequence[T]:`