Update readme. (envoyproxy#152)

mixerclient/README.md

@@ -1,2 +1,15 @@
-# mixerclient
-C++ client for the mixer API
+# Istio Mixerclient
+
+The Istio Mixerclient is a C++ library to support the mixer API with following features:
+
+- Uses simple struct Attributes to pass attributes. The library will convert them to the request proto message by using the global dictionary and per message dictionary.
+
+- Supports combining multiple quota calls into one single Check call together with precondition check.
+
+- Supports cache for precondition check result. Attributes used to calculate cache key are specified by the Mixer. By default, check cache is enabled unless CheckOptions.num_entries is 0.
+
+- Supports quota cache and prefetch. Attributes used to calculate quota cache key are specified by the Mixer too. By default, quota cache is enabled unless QuotaOptions.num_entries is 0.
+
+- Supports batch for Reports. All report requests are batched up to ReportOptions.max_batch_entries, or up to ReportOptions.max_match_time_ms.
+
+