Add PETPrep tool for PET data preprocessing

Added PETPrep entry with details for preprocessing PET data.

Author: mnoergaard

data/tools/apps.yml

@@ -428,6 +428,17 @@ apps:
     -   func
     description:
 
+-   gh: nipreps/petprep
+    status: active
+    dh: nipreps/petprep
+    ds_type:
+    -   raw
+    datatype:
+    -   anat
+    -   pet
+    description: PETPrep is a robust and easy-to-use pipeline for preprocessing of diverse PET data. The transparent workflow dispenses of manual intervention,
+        thereby ensuring the reproducibility of the results.
+
 -   gh: nipreps/smriprep
     status: active
     dh: nipreps/smriprep