added missing "dihedral" in compute dihedral/local docs

doc/src/compute_dihedral_local.txt

@@ -27,8 +27,8 @@ compute 1 all dihedral/local phi :pre
 
 Define a computation that calculates properties of individual dihedral
 interactions.  The number of datums generated, aggregated across all
-processors, equals the number of angles in the system, modified by the
-group parameter as explained below.
+processors, equals the number of dihedral angles in the system, modified
+by the group parameter as explained below.
 
 The value {phi} is the dihedral angle, as defined in the diagram on
 the "dihedral_style"_dihedral_style.html doc page.