Add license file to README.fuchsia

Change-Id: I3651bed8dc62a9440d8ac236ba9bf4ccab450b6e
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/tink/+/913557
Reviewed-by: Jerry Belton <jcecil@google.com>
Fuchsia-Auto-Submit: Yaar Schnitman <yaar@google.com>
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>
diff --git a/README.fuchsia b/README.fuchsia
index 1c0c5e3..b598eaf 100644
--- a/README.fuchsia
+++ b/README.fuchsia
@@ -1,3 +1,4 @@
 Name: Tink
 URL: https://github.com/google/tink
 LICENSE: Apache 2.0 license
+License File: LICENSE