HDFFV-10384 Add opt arg to help

tools/testfiles/pbits/tpbitsOffsetExceeded.ddl

@@ -44,8 +44,8 @@ usage: h5dump [OPTIONS] files
      -m T, --format=T     Set the floating point output format
      -q Q, --sort_by=Q    Sort groups and attributes by index Q
      -z Z, --sort_order=Z Sort groups and attributes by order Z
-     --enable-error-stack Prints messages from the HDF5 error stack as they
-                          occur.
+     --enable-error-stack Prints messages from the HDF5 error stack as they occur.
+                          Optional value 2 also prints file open errors.
      --no-compact-subset  Disable compact form of subsetting and allow the use
                           of "[" in dataset names.
      -w N, --width=N      Set the number of columns of output. A value of 0 (zero)