lib/cli/create_db: make WAL mode optional

lib/cli/commands/create_db.dart

@@ -12,6 +12,16 @@ class CreateDb extends Command {
 
   CreateDb() {
     addLibsqliteArg(argParser);
+    argParser.addFlag(
+      'wal',
+      help:
+          '''Whether to use Write-Ahead Logging (WAL) mode.
+
+          This is recommended for better performance, but may not be used with
+          the readonly NixOS store.
+      ''',
+      defaultsTo: false,
+    );
   }
 
   Future<void> run() async {
@@ -22,6 +32,7 @@ class CreateDb extends Command {
 
     final db = await openLocalDb(
       libsqlitePath: argResults!.option('libsqlite')!,
+      walMode: argResults!.flag('wal'),
       readWrite: true,
     );