Merge branch 'develop' into 0.3.0

Former-commit-id: 84fd081536835f30938fc92340220fa2d9ce4813 [formerly 9e4bd58615ab42ad180372ffdd36c3a0136821e7]
Former-commit-id: eaa6cbe8bfc582e611edf08dca6c9e422dbfe073
diff --git a/docs/index.md b/docs/index.md
index b7b6fe6..a7d5032 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -19,10 +19,11 @@
 * [Response](user/response.md)
 * [Api Model](user/api.md)
 * [Installation](user/installation.md)
+* [Metric](user/metric.md)
 
 ## [Developer Guide](developer/README.md)
 
 * [Concept](developer/concept.md)
 * [Auto Registry](developer/auto-registy.md)
 * [Filter](developer/filter.md)
-* [Log](developer/log.md)
\ No newline at end of file
+* [Log](developer/log.md)
diff --git a/docs/user/metric.md b/docs/user/metric.md
new file mode 100644
index 0000000..dd0b395
--- /dev/null
+++ b/docs/user/metric.md
@@ -0,0 +1,11 @@
+# Metric
+
+## Enable
+You can enable the metric in config.yaml as follows.         
+Config pixiu's ip and prometheus_port below in your prometheus config file 
+will allow prometheus to scrape the metric generated by pixiu.
+```yaml
+metric:
+  enable: true
+  prometheus_port: 2222
+```