TOC: fix breakage from pingcap#1045 (pingcap#1050)

The features linked to overview.md

Author: morgo

TOC.md

@@ -6,23 +6,23 @@
 + Concepts
   - [Architecture](architecture.md)
   + [Key Features](key-features.md)
-    - [Horizontal Scalability](overview.md#horizontal-scalability)
-    - [MySQL Compatible Syntax](overview.md#mysql-compatible-syntax)
-    - [Replicate from and to MySQL](overview.md#replicate-from-and-to-mysql)
-    - [Distributed Transactions with Strong Consistency](overview.md#distributed-transactions-with-strong-consistency)
-    - [Cloud Native Architecture](overview.md#cloud-native-architecture)
-    - [Minimize ETL with HTAP](overview.md#minimize-etl-with-htap)
-    - [Fault Tolerance & Recovery with Raft](overview.md#fault-tolerance--recovery-with-raft)
-    - [Automatic Rebalancing](overview.md#automatic-rebalancing)
-    - [Deployment and Orchestration with Ansible, Kubernetes, Docker](overview.md#deployment-and-orchestration-with-ansible-kubernetes-docker)
-    - [JSON Support](overview.md#json-support)
-    - [Spark Integration](overview.md#spark-integration)
-    - [Read Historical Data without Restoring from Backup](overview.md#read-historical-data-without-restoring-from-backup)
-    - [Fast Import and Restore of Data](overview.md#fast-import-and-restore-of-data)
-    - [Hybrid of Column and Row Storage](overview.md#hybrid-of-column-and-row-storage)
-    - [SQL Plan Management](overview.md#sql-plan-management)
-    - [Open Source](overview.md#open-source)
-    - [Online Schema Changes](overview.md#online-schema-changes)
+    - [Horizontal Scalability](key-features.md#horizontal-scalability)
+    - [MySQL Compatible Syntax](key-features.md#mysql-compatible-syntax)
+    - [Replicate from and to MySQL](key-features.md#replicate-from-and-to-mysql)
+    - [Distributed Transactions with Strong Consistency](key-features.md#distributed-transactions-with-strong-consistency)
+    - [Cloud Native Architecture](key-features.md#cloud-native-architecture)
+    - [Minimize ETL with HTAP](key-features.md#minimize-etl-with-htap)
+    - [Fault Tolerance & Recovery with Raft](key-features.md#fault-tolerance--recovery-with-raft)
+    - [Automatic Rebalancing](key-features.md#automatic-rebalancing)
+    - [Deployment and Orchestration with Ansible, Kubernetes, Docker](key-features.md#deployment-and-orchestration-with-ansible-kubernetes-docker)
+    - [JSON Support](key-features.md#json-support)
+    - [Spark Integration](key-features.md#spark-integration)
+    - [Read Historical Data without Restoring from Backup](key-features.md#read-historical-data-without-restoring-from-backup)
+    - [Fast Import and Restore of Data](key-features.md#fast-import-and-restore-of-data)
+    - [Hybrid of Column and Row Storage](key-features.md#hybrid-of-column-and-row-storage)
+    - [SQL Plan Management](key-features.md#sql-plan-management)
+    - [Open Source](key-features.md#open-source)
+    - [Online Schema Changes](key-features.md#online-schema-changes)
 + How-to
   + Get Started
     + Start a Local Cluster