Update README with proper `cargo test` command
We don't need to run the rust tests single-threaded anymore.
@@ -163,7 +163,7 @@ If you want to use the command line, start `sbt` in
- Start all test databases with `make all-dbs`.
**Run:**
-Run `cargo test -- --test-threads 1` in the repository root.
+Run `cargo test` in the repository root.
## WIP Coding Guidelines
- Prevent compiler warnings
