Explain usages of .memory() in docs

docs/pages/docs/Advanced Features/isolates.md

@@ -18,10 +18,13 @@ targets:
         options:
           generate_connect_constructor: true
 ```
+
 Next, re-run the build. You can now add another constructor to the generated database class:
+
 ```dart
 @DriftDatabase(...)
 class TodoDb extends _$TodoDb {
+  // Your existing constructor, whatever it may be...
   TodoDb() : super(NativeDatabase.memory());
 
   // this is the new constructor

docs/pages/docs/Using SQL/moor_files.md

@@ -24,6 +24,8 @@ part 'database.g.dart';
   include: {'tables.drift'},
 )
 class MyDb extends _$MyDb {
+  // This example creates a simple in-memory database (without actual persistence).
+  // To actually store data, see the database setups from other "Getting started" guides.
   MyDb() : super(NativeDatabase.memory());
 
   @override