CHANGELOG.md: add file, explain open-policy-agent#256

Signed-off-by: Stephan Renatus <[email protected]>

Author: srenatus

CHANGELOG.md

@@ -0,0 +1,19 @@
+# Change Log
+
+All notable changes to this project will be documented in this file. This
+project adheres to [Semantic Versioning](http://semver.org/).
+
+## Unreleased
+
+### Fixes
+
+- Support escaped forward-slashes (`\/`) in JSON request bodies (#256, @Dakatan).
+
+  When parsing request bodies of requests with header "Content-Type: application/json",
+  opa-envoy-plugin had used a utility method from github.com/open-policy-agent/opa that
+  also accepted YAML. This wasn't an intentional feature, and has been removed.
+
+  One side-effect of using that method was that an escaped forward slash, which is
+  allowed in the JSON spec (but optional, forward slashes *may* be escaped), wasn't
+  parsed properly, leading to a denying policy response when the request may have
+  been permissible.