correct link for dispersion parameter how-to and reformat

doc/src/kspace_modify.txt

@@ -290,9 +290,10 @@ to be specified using the {gewald/disp}, {mesh/disp},
 {force/disp/real} or {force/disp/kspace} keywords, or
 the code will stop with an error message. When this option is set to
 {yes}, the error message will not appear and the simulation will start.
-For a typical application, using the automatic parameter generation will provide
-simulations that are either inaccurate or slow. Using this option is thus not
-recommended. For guidelines on how to obtain good parameters, see the "How-To"_Section_howto.html#howto_23 discussion.
+For a typical application, using the automatic parameter generation
+will provide simulations that are either inaccurate or slow. Using this
+option is thus not recommended. For guidelines on how to obtain good
+parameters, see the "How-To"_Section_howto.html#howto_24 discussion.
 
 [Restrictions:] none