docs: Fix readyset invocation in community development guide

The instructions for starting readyset specified `--username` and
`--password` parameters, but those are deprecated.  The credentials are
passed in the `--upstream-db-url` parameter instead.

Change-Id: Id5d5986aa266d182fbad509bd503ef5c6a6a6964
Reviewed-on: https://gerrit.readyset.name/c/readyset/+/11164
Reviewed-by: Gautam Gopinadhan <gautam@readyset.io>
Tested-by: Buildkite CI

Author: ronh-rs

community-development.md

@@ -79,13 +79,13 @@ storage.
    **Run against Postgres:**
 
    ```bash
-   cargo run --bin readyset --release -- --database-type=postgresql --upstream-db-url=postgresql://postgres:readyset@127.0.0.1:5432/testdb --username=postgres --password=readyset --address=0.0.0.0:5433 --deployment=<deployment name> --prometheus-metrics
+   cargo run --bin readyset --release -- --database-type=postgresql --upstream-db-url=postgresql://postgres:readyset@127.0.0.1:5432/testdb  --address=0.0.0.0:5433 --deployment=<deployment name> --prometheus-metrics
    ```
 
    **Run against MySQL:**
 
    ```bash
-   cargo run --bin readyset --release -- --database-type=mysql --upstream-db-url=mysql://root:readyset@127.0.0.1:3306/testdb --username=root --password=readyset --address=0.0.0.0:3307 --deployment=<deployment name> --prometheus-metrics
+   cargo run --bin readyset --release -- --database-type=mysql --upstream-db-url=mysql://root:readyset@127.0.0.1:3306/testdb --address=0.0.0.0:3307 --deployment=<deployment name> --prometheus-metrics
    ```
 
    This runs the Readyset Server and Adapter as a single process, a simple, standard way to run Readyset that is also the easiest approach when developing. For production deployments, however, it is possible to run the Server and Adapter as separate processes. See the [scale out deployment pattern](https://docs.readyset.io/guides/deploy/production-notes/#scale-out) in the docs.