Update metadata.md

Add section references

Author: hyanwong

metadata.md

@@ -73,6 +73,7 @@ import json
 
 ts = tskit.load("data/metadata.trees")
 ```
+(sec_tutorial_metadata_reading)=
 
 ## Reading metadata and schemas
 
@@ -107,6 +108,8 @@ If there is no schema (i.e. it is equal to ``MetadataSchema(None)``) for a table
 or top-level metadata, then no decoding is performed and ``bytes`` will be returned.
 :::
 
+(sec_tutorial_metadata_modifying)=
+
 ## Modifying metadata and schemas
 
 If you are creating or modifying a tree sequence by changing the underlying tables,
@@ -200,6 +203,8 @@ print(tables.individuals[new_id].metadata)
 
 To modify the metadata of rows in tables use the {ref}`sec_tutorial_metadata_bulk`.
 
+(sec_tutorial_metadata_viewing_raw)=
+
 ## Viewing raw metadata
 
 If you need to see the raw (i.e. bytes) metadata, you just need to remove the