gnu: rav1e: Mark as tunable.

* gnu/packages/video.scm (rav1e)[properties]: Mark package as tunable.

Change-Id: Icaf3615ce6f1e76416543a1285af5f1fdaec3589

gnu/packages/video.scm

@@ -6021,6 +6021,8 @@ result in several formats:
     (description "@code{rav1e} is an AV1 video encoder.  It is designed to
 eventually cover all use cases, though in its current form it is most suitable
 for cases where libaom (the reference encoder) is too slow.")
+    ;; This package shows a large speed boost when tuned for newer architectures.
+    (properties `((tunable? . #t)))
     (license license:bsd-2)))
 
 (define-public peek