Bazel: export LICENSE file.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>
diff --git a/BUILD b/BUILD
index b36ce25..e3db970 100644
--- a/BUILD
+++ b/BUILD
@@ -36,6 +36,8 @@
 
 licenses(["notice"])  # 3-clause BSD
 
+exports_files(["LICENSE"])
+
 package(default_visibility = ["//visibility:public"])