Update config_spec.md
Remove `evaluation_units` from mandatory fields in EVALUATION section
This field is actually in application SEGMENTATION field, as shown in the source
code The args that get parsed is `self.app_param` instead of `self.eval_param`
@@ -718,8 +718,13 @@ The evaluation configuration section (`[EVALUATION]`) must contain:
[regression evaluations](./niftynet.evaluation.regression_evaluations.html),
[segmentation evaluations](./niftynet.evaluation.segmentation_evaluations.html),
and [classification evaluations](./niftynet.evaluation.classification_evaluations.html).
+
+Note that application specific configuration (such as `evaluation_units`) are specified
+in the application configuration section (such as `[SEGMENTATION]`).
+<!---
- `evaluation_units` -- `foreground`, `label` or `cc`. Describe how the
evaluation should be performed in the case of segmentation mostly
(`foreground` means only one label, `label` means metrics per label, `cc`
means metrics per connected component). More on this topic can be found at
[segmentation evaluations](./niftynet.evaluation.segmentation_evaluations.html).
+-->
