Document import/export notes for WAL databases

docs/pages/docs/Examples/existing_databases.md

@@ -89,6 +89,16 @@ class MyDatabase extends _$MyDatabase {
   // ...
 ```
 
+### Additional considerations for WAL
+
+When enabling [write-ahead logging](https://www.sqlite.org/wal.html), sqlite3 won't immediately
+store all writes in the main database file. Instead, additional `-wal` and `-shm` files are
+created to append new writes that are then periodically synced into the main database file.
+
+Restoring a WAL database requires copying the `-wal` file as well.
+When overwriting an existing WAL database on the device with a database using a different
+journaling mode, the `-wal` file should be deleted too.
+
 ## Exporting a database
 
 To export a sqlite3 database into a file, you can use the `VACUUM INTO` statement.

docs/pages/docs/Platforms/vm.md

@@ -106,6 +106,8 @@ LazyDatabase(() async {
 });
 ```
 
+Using existing databases is explained in more detail in [this example]({{ '../Examples/existing_databases.md' | pageUrl }}).
+
 ## Used compile options on Android
 
 On Android, iOS and macOs, depending on `sqlite3_flutter_libs` will include a custom build of sqlite instead of