[Positioner] CSVStringReader: doc improvement

Improve the description of CSVStringReader::read_point3d().

owlps-positioner/csvstringreader.cc

@@ -115,6 +115,12 @@ bool CSVStringReader::read_timestamp(Timestamp &t)
 /**
  * The first field (X) can start with an opening parenthesis, and the
  * last one (Z) can finish with a closing parenthesis.
+ *
+ * @param[out] p The variable in which the read Point3D will be stored.
+ * It is left untouched if a full Point3D cannot be read successfuly.
+ *
+ * @returns `true` if the Point3D was read successfuly.
+ * @returns `false` in case of error.
  */
 bool CSVStringReader::read_point3d(Point3D &p)
 {