Update README.md (#5185)

README.md

@@ -46,13 +46,16 @@ SkyWalking OAP is using the STAM(Streaming Topology Analysis Method) to analysis
 for better performance. Read [the paper of STAM](https://wu-sheng.github.io/STAM/) for more details.
 
 # Document
-[8.x dev](docs/README.md),
-[8.1.0](https://github.com/apache/skywalking/blob/v8.1.0/docs/README.md),  
-[8.0.1](https://github.com/apache/skywalking/blob/v8.0.1/docs/README.md), 
-[8.0.0](https://github.com/apache/skywalking/blob/v8.0.0/docs/README.md) 
-| [7.0](https://github.com/apache/skywalking/blob/v7.0.0/docs/README.md) 
-| [6.6](https://github.com/apache/skywalking/blob/v6.6.0/docs/README.md), 
-[6.5](https://github.com/apache/skywalking/blob/v6.5.0/docs/README.md).
+Version Series | Version | 
+----------- | ---------- |
+8.x| [8.x dev](docs/README.md)|
+| | [8.1.0](https://github.com/apache/skywalking/blob/v8.1.0/docs/README.md) |
+| | [8.0.1](https://github.com/apache/skywalking/blob/v8.0.1/docs/README.md) |
+| | [8.0.0](https://github.com/apache/skywalking/blob/v8.0.0/docs/README.md) |
+7.x | [7.0](https://github.com/apache/skywalking/blob/v7.0.0/docs/README.md) |
+6.x | [6.6](https://github.com/apache/skywalking/blob/v6.6.0/docs/README.md) |
+| | [6.5](https://github.com/apache/skywalking/blob/v6.5.0/docs/README.md) |
+
 
 NOTICE, SkyWalking 8.0+ uses [v3 protocols](docs/en/protocols/README.md). They are incompatible with previous releases.