Add suggestions for creating test cases

```
Not to select pose that planner gets hard to calculate path is better for perception pipeline. Because we are measuring for middleware, not for planner. Should i add this part to documentation, @sjahr ?
```
_Originally posted by @CihatAltiparmak  in https://github.com/CihatAltiparmak/moveit_middleware_benchmark/pull/5#discussion_r1664972688_