Fixed links in schema doc

com.unity.perception/Documentation~/Schema/Synthetic_Dataset_Schema.md

 }
 ```
 ##### semantic segmentation
-Annotation spec for semantic segmentation labeler([see semantic segmentation](#semanticsegmentation)).
+Annotation spec for semantic [segmentation labeler](#semantic-segmentation---grayscale-image)
 ```
 annotation_definition.spec {        
   label_id:          <int>           -- Integer identifier of the label
 }
 ```
 ##### label enumeration spec
-This spec is used for annotations like bounding box 2d. This might be a subset of all labels used in simulation ([see bounding box 2D](#2Dboundingbox)).
+This spec is used for annotations like [bounding box 2d](#2d-bounding-box). This might be a subset of all labels used in simulation ([see bounding box 2D](#2Dboundingbox)).
 ```
 annotation_definition.spec {
   label_id:          <int>           -- Integer identifier of the label
 ##### keypoint template
-keypoint templates are used to define the keypoints and skeletal connections captured by the keypoint labeler ([see keypoint](#keypoints)).
+keypoint templates are used to define the keypoints and skeletal connections captured by the [keypoint labeler](#keypoints).
 ```
 annotation_definition.spec {
   template_id:       <str>           -- The UUID of the template