Bazel: export LICENSE file.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>
diff --git a/BUILD b/BUILD
index c0ac6d8..be1af17 100644
--- a/BUILD
+++ b/BUILD
@@ -7,6 +7,8 @@
 
 licenses(["notice"])  # MIT
 
+exports_files(["LICENSE"])
+
 STRICT_C_OPTIONS = [
     "--pedantic-errors",
     "-Wall",