Better sample command for hammer (#138)

The previous version had a smaller number of writers than operations to perform, which meant it was often blocked until a batch was flushed. This updates the sample command to values that leave the hammer always performing work instead of blocking.

hammer/README.md

@@ -22,7 +22,10 @@ Example usage to test a deployment of `example-mysql`:
 go run ./hammer \
   --log_public_key=Test-Betty+df84580a+AQQASqPUZoIHcJAF5mBOryctwFdTV1E0GRY4kEAtTzwB \
   --log_url=http://localhost:2024 \
-  --num_writers=22 \
+  --max_read_ops=1024 \
+  --num_readers_random=128 \
+  --num_readers_full=128 \
+  --num_writers=256 \
   --max_write_ops=42
 ```