Add clarifying comment to partial database class

docs/lib/snippets/setup/database.dart

@@ -31,7 +31,12 @@ class TodoItems extends Table {
 
 @DriftDatabase(tables: [TodoItems])
 class AppDatabase extends _$AppDatabase {
+// #enddocregion open
+  // After generating code, this class needs to define a `schemaVersion` getter
+  // and a constructor telling drift where the database should be stored.
+  // These are described in the getting started guide: https://drift.simonbinder.eu/getting-started/#open
 // #enddocregion before_generation
+// #docregion open
   AppDatabase() : super(_openConnection());
 
   @override

docs/pages/docs/setup.md

@@ -99,7 +99,7 @@ You will now see errors related to missing overrides and a missing constructor.
 is responsible for telling drift how to open the database. The `schemaVersion` getter is relevant
 for migrations after changing the database, we can leave it at `1` for now. The database class
 now looks like this:
-
+<a name="open">
 {% include "blocks/snippet" snippets = snippets name = 'open' %}
 
 The Android-specific workarounds are necessary because sqlite3 attempts to use `/tmp` to store