Modernised the collector_config schema description

Author: Jamesbarford

database/schema.md

@@ -298,12 +298,18 @@ Columns:
 
 ### collector_config
 
-Information about the collector; it's target architecture, when it was added, whether it is active and when it last had activity denoted by `last_heartbeat_at`.
+Information about the collector; it's target architecture, when it was added,
+whether it is active and when it last had activity denoted by `last_heartbeat_at`.
 
-```
-sqlite> SELECT * FROM collector_config;
+Columns:
 
-id         target                     name  date_added     last_heartbeat_at  benchmark_set  is_active
----------  -------------------------  ----  -------------  ----------------   ---------      -------
-1          aarch64-unknown-linux-gnu  foo   2025-06-11...  2025-06-12 17...   2              0
-```
+* **id** (`id`): A unique identifier for the collector.
+* **target** (`text NOT NULL`): The ISA of the collector for example; `AArch64`.
+* **name** (`text NOT NULL`): Unique name for the collector.
+* **date_added** (`timestamptz NOT NULL`): When the collector was added
+* **last_heartbeat_at** (`timestamptz`): When the collector last updated this
+  column, a way to test if the collector is still alive.
+* **benchmark_set** (`int NOT NULL`): ID of the predefined benchmark suite to
+  execute.
+* **is_active** (`boolean NOT NULL`): For controlling whether the collector is
+  active for use. Useful for adding/removing collectors.