what-is-nebula-graph (#523)

* what-is-nebula-graph

* Address Wum's Comments

docs-2.0/1.introduction/1.what-is-nebula-graph.md

@@ -20,10 +20,18 @@ Nebula Graph is open under the Apache 2.0 and the Commons Clause 1.0 licenses. M
 
 Written in C++ and born for graph, Nebula Graph handles graph queries in milliseconds. Among most databases, Nebula Graph shows superior performance in providing graph data services. The larger the data size, the greater the superiority of Nebula Graph. For more information, see [Nebula Graph benchmarking](https://discuss.nebula-graph.io/t/nebula-graph-1-0-benchmark-report/581).
 
+### High scalability
+
+Nebula Graph is designed in a shared-nothing architecture and supports scaling in and out without interrupting the database service.
+
 ### Developer friendly
 
 Nebula Graph supports clients in popular programming languages like Java, Python, C++, and Go, and more are being developed. For more information, see Nebula Graph [clients](../20.appendix/6.eco-tool-version.md).
 
+### Reliable access control
+
+Nebula Graph supports strict role-based access control and external authentication servers such as LDAP (Lightweight Directory Access Protocol) servers to enhance data security. For more information, see [Authentication and authorization](../7.data-security/1.authentication/1.authentication.md).
+
 ### Diversified ecosystem
 
 More and more native tools of Nebula Graph have been released, such as [Nebula Graph Studio](https://github.com/vesoft-inc/nebula-web-docker), [Nebula Console](https://github.com/vesoft-inc/nebula-console), and [Nebula Exchange](https://github.com/vesoft-inc/nebula-spark-utils/tree/v2.0.0/nebula-exchange). Besides, Nebula Graph has the ability to be integrated with many cutting-edge technologies, such as Spark, Flink, and HBase, for the purpose of mutual strengthening in a world of increasing challenges and chances. For more information, see [Ecosystem development](../20.appendix/6.eco-tool-version.md).
@@ -36,14 +44,6 @@ The native Nebula Graph Query Language, also known as nGQL, is a declarative, op
 
 You can easily model the connected data into Nebula Graph for your business without forcing them into a structure such as a relational table, and properties can be added, updated, and deleted freely. For more information, see [Data modeling](2.data-model.md).
 
-### Reliable access control
-
-Nebula Graph supports strict role-based access control and external authentication servers such as LDAP (Lightweight Directory Access Protocol) servers to enhance data security. For more information, see [Authentication and authorization](../7.data-security/1.authentication/1.authentication.md).
-
-### High scalability
-
-Nebula Graph is designed in a shared-nothing architecture and supports scaling in and out without interrupting the database service.
-
 ### High popularity
 
 Nebula Graph is being used by tech leaders such as Tencent, Vivo, Meituan, and JD Digits. For more information, visit the [Nebula Graph official website](https://nebula-graph.io/).
@@ -67,3 +67,11 @@ Natural languages can be transformed into knowledge graphs and stored in Nebula
 ### Social networking
 
 Information on people and their relationships are typical graph data. Nebula Graph can easily handle the social networking information of billions of people and trillions of relationships, and provide lightning-fast queries for friend recommendations and job promotions in the case of massive concurrency.
+
+## Related links
+
+- [Official website](https://www.vesoft.com/en/)
+- [Docs](https://docs.nebula-graph.io/master/)
+- [Blog](https://nebula-graph.io/posts/)
+- [Forum](https://discuss.nebula-graph.io)
+- [GitHub](https://github.com/vesoft-inc)