update contrib readme (#1831)

encoding/README.md

@@ -0,0 +1,7 @@
+# encoding
+
+## msgpack
+
+```shell
+go get -u github.com/go-kratos/kratos/contrib/encoding/msgpack/v2
+```

log/README.md

@@ -48,3 +48,9 @@ go get -u github.com/go-kratos/kratos/contrib/log/zap/v2
 ```shell
 go get -u github.com/go-kratos/kratos/contrib/log/fluent/v2
 ```
+
+### aliyun
+
+```shell
+go get -u github.com/go-kratos/kratos/contrib/log/aliyun/v2
+```

registry/README.md

@@ -1,26 +1,37 @@
 # Registry
 
 ## Consul
+
 ```shell
 go get -u github.com/go-kratos/kratos/contrib/registry/consul/v2
 ```
 
 ## Etcd
+
 ```shell
 go get -u github.com/go-kratos/kratos/contrib/registry/etcd/v2
 ```
 
 ## zookeeper
+
 ```shell
 go get -u github.com/go-kratos/kratos/contrib/registry/zookeeper/v2
 ```
 
 ## Nacos
+
 ```shell
 go get -u github.com/go-kratos/kratos/contrib/registry/nacos/v2
 ```
 
 ## kubernetes
+
 ```shell
 go get -u github.com/go-kratos/kratos/contrib/registry/kubernetes/v2
 ```
+
+## polaris
+
+```shell
+go get -u github.com/go-kratos/kratos/contrib/registry/polaris/v2
+```