Add Appveyor badge.
diff --git a/README.md b/README.md
index cc9fdfb..5730ddc 100644
--- a/README.md
+++ b/README.md
@@ -31,4 +31,5 @@
If you want to reach the authors in private, use <libzip@nih.at>.

+[](https://ci.appveyor.com/project/0-wiz-0/libzip)
