add versionadded tag to new inputs keyword docs

doc/src/compute_reduce.rst

@@ -201,6 +201,8 @@ information in this context, the *replace* keywords will extract the
 atom IDs for the two atoms in the bond of maximum stretch.  These atom
 IDs and the bond stretch will be printed with thermodynamic output.
 
+.. versionadded:: TBD
+
 The *inputs* keyword allows selection of whether all the inputs are
 per-atom or local quantities.  As noted above, all the inputs must be
 the same kind (per-atom or local).  Per-atom is the default setting.