Have you thought of enabling WAL mode for SQLite?

Have you thought of enabling SQLite's [Write-Ahead Logging](https://sqlite.org/wal.html)?

This allows simultaneous writes and reading, which would improve the performance when using SQLite with no real downside.

I've done this in other Django projects using the `connection_created` signal (see example below). I'd be happy to make this change and open a pull request, if you'd like.

```
@receiver(connection_created)
def setup_sqlite(connection, **kwargs):
if connection.vendor != "sqlite":
return

with connection.cursor() as cursor:
cursor.execute("pragma journal_mode = WAL;")
cursor.execute("pragma synchronous = normal;")
cursor.execute("pragma temp_store = memory;")
cursor.execute("pragma mmap_size = 256000000;")
```