Change default format for ecosystem checks to markdown (#8412)

To facilitate easier local runs

python/ruff-ecosystem/README.md

@@ -31,6 +31,9 @@ Run `ruff format` ecosystem checks comparing your debug build to your system Ruf
 ruff-ecosystem format ruff "./target/debug/ruff"
 ```
 
+The default output format is markdown, which includes nice summaries of the changes. You can use `--output-format json` to display the raw data — this is
+particularly useful when making changes to the ecosystem checks.
+
 ## Development
 
 When developing, it can be useful to set the `--pdb` flag to drop into a debugger on failure:

python/ruff-ecosystem/ruff_ecosystem/cli.py

@@ -121,7 +121,7 @@ def parse_args() -> argparse.Namespace:
     parser.add_argument(
         "--output-format",
         choices=[option.name for option in OutputFormat],
-        default="json",
+        default="markdown",
         help="Location for caching cloned repositories",
     )
     parser.add_argument(