make markdownlint happier

VENDORED_CODE.md

@@ -1,12 +1,14 @@
+# Use of vendored code in Weave Net
+
 Weave Net is licensed under the [Apache 2.0 license](LICENSE).
 
 Some vendored code is under different licenses though, all of them ship the
 entire license text they are under.
 
- - https://github.com/weaveworks/go-checkpoint
+- https://github.com/weaveworks/go-checkpoint
   can be found in the ./vendor/ directory, is under MPL-2.0.
 
- - Pulled in by dependencies are
+- Pulled in by dependencies are  
   https://github.com/hashicorp/golang-lru (MPL-2.0)  
   https://github.com/hashicorp/go-cleanhttp (MPL-2.0)  
   https://github.com/opencontainers/go-digest (docs are under CC by-sa 4.0)