Fix dangling URI (#464)

Author: chenziliang

docs/mutable-stream.md

@@ -69,17 +69,17 @@ Data is first ingested into the WAL, and then asynchronously committed to the ro
 
 The Mutable Stream settings allow fine-tuning of both storage layers to balance performance, durability, and efficiency.
 
-### Secondary Indexes
-
-See the [Secondary Indexes](/mutable-stream-secondary-index) documentation for details.
-
 ### PRIMARY KEY
 
 **PRIMARY KEY** — Defines the uniqueness of a row in a Mutable Stream. **Required.**  
 
 Rows are organized and sorted based on the primary key, and the primary index is built on top of it.  
 See [Mutable Stream Indexes](/mutable-stream-indexes) for more details.  
 
+### Secondary Indexes
+
+See the [Mutable Stream Indexes](/mutable-stream-indexes) documentation for details.
+
 ### Settings
 
 #### `shards`