Add macaroone implementation from
    https://weave.googlesource.com/weave/libuweave

BUG:25934771
Change-Id: Iba87e709a51006f3e966b9942a375d1c31b2f17d
Reviewed-on: https://weave-review.googlesource.com/1804
Reviewed-by: Alex Vakulenko <avakulenko@google.com>
diff --git a/third_party/libuweave/README b/third_party/libuweave/README
new file mode 100644
index 0000000..f170307
--- /dev/null
+++ b/third_party/libuweave/README
@@ -0,0 +1,4 @@
+URL: https://weave.googlesource.com/weave/libuweave/+/master
+
+Description:
+Macaroon related code from libuweave.