chore: add one more example into the placeholder (#10)

Author: NGA-TRAN

src/features/plan-visualizer/components/PlanInput.tsx

@@ -52,7 +52,7 @@ export function PlanInput({
           value={value}
           onChange={(e) => onChange(e.target.value)}
           onKeyDown={handleKeyDown}
-          placeholder={`Paste your DataFusion Physical Execution Plan here...\n\nExample:\nProjectionExec: expr=[id@0 as id]\n  FilterExec: id@0 > 100\n    ParquetExec: file_groups={...}`}
+          placeholder={`Paste your DataFusion Physical Execution Plan here...\n\nExample 1 (Physical Plan only):\nProjectionExec: expr=[id@0 as id]\n  FilterExec: id@0 > 100\n    ParquetExec: file_groups={...}\n\nExample 2 (Full EXPLAIN output):\nEXPLAIN SELECT * FROM dim;\n+---------------+---------------------------------------------------------------------------------------------------------------------+\n| plan_type     | plan                                                                                                                |\n+---------------+---------------------------------------------------------------------------------------------------------------------+\n| logical_plan  | TableScan: dim2_parquet projection=[d_dkey, env, service, host]                                                     |\n| physical_plan | DataSourceExec: file_groups={1 groups: [[d_1.parquet]]}, projection=[d_dkey, env, service, host], file_type=parquet |\n+---------------+---------------------------------------------------------------------------------------------------------------------+`}
           className={cn(
             'w-full h-full min-h-[150px] sm:min-h-[200px] p-3 sm:p-4 font-mono text-xs sm:text-sm',
             'bg-gray-50 dark:bg-gray-800/50',