add some comments

extra/entrypoint.sh

@@ -1,10 +1,14 @@
 #!/usr/bin/env sh
 
+# set -e Exit the script if an error happens
 set -e
 PUID=${PUID=1000}
 PGID=${PGID=1000}
 
 files_ownership () {
+    # -h Changes the ownership of an encountered symbolic link and not that of the file or directory pointed to by the symbolic link.
+    # -R Recursively descends the specified directories
+    # -c Like verbose but report only when a change is made
     chown -hRc "$PUID":"$PGID" /app/data
 }
 
@@ -12,4 +16,6 @@ echo "==> Performing startup jobs and maintenance tasks"
 files_ownership
 
 echo "==> Starting application with user $PUID group $PGID"
+
+# --clear-groups Clear supplementary groups.
 exec setpriv --reuid "$PUID" --regid "$PGID" --clear-groups "$@"