Storage: add chunks_head and fix links (#7693)

The links fix makes the links point to the current version of the files,
e.g. the relase branch.

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

docs/storage.md

@@ -37,17 +37,20 @@ The directory structure of a Prometheus server's data directory will look someth
 │   ├── tombstones
 │   ├── index
 │   └── meta.json
+├── chunks_head
+│   └── 000001
 └── wal
-    ├── 00000002
-    └── checkpoint.000001
+    ├── 000000002
+    └── checkpoint.00000001
+        └── 00000000
 ```
 
 
-Note that a limitation of the local storage is that it is not clustered or replicated. Thus, it is not arbitrarily scalable or durable in the face of disk or node outages and should be treated as you would any other kind of single node database. Using RAID for disk availability, [snapshots](https://prometheus.io/docs/prometheus/latest/querying/api/#snapshot) for backups, capacity planning, etc, is recommended for improved durability. With proper storage durability and planning storing years of data in the local storage is possible.
+Note that a limitation of the local storage is that it is not clustered or replicated. Thus, it is not arbitrarily scalable or durable in the face of disk or node outages and should be treated as you would any other kind of single node database. Using RAID for disk availability, [snapshots](querying/api.md#snapshot) for backups, capacity planning, etc, is recommended for improved durability. With proper storage durability and planning storing years of data in the local storage is possible.
 
 Alternatively, external storage may be used via the [remote read/write APIs](https://prometheus.io/docs/operating/integrations/#remote-endpoints-and-storage). Careful evaluation is required for these systems as they vary greatly in durability, performance, and efficiency.
 
-For further details on file format, see [TSDB format](https://github.com/prometheus/prometheus/blob/master/tsdb/docs/format/README.md).
+For further details on file format, see [TSDB format](/tsdb/docs/format/README.md).
 
 ## Compaction