doc: ug_troubleshooting: reorder "Debugging hints" section

Most "utilities" mentioned in the "debugging hints" section are namelist
flags, and so the introductory sentence about some "not working
everywhere in the code" is misleading, since this sentence applies to
subroutines.

Reorganize this section by adding two subheaders, first "Namelist flags"
and then "Subroutines". Move the sentence about subroutines not working
from everywhere in the code to this second section.

doc/source/user_guide/ug_troubleshooting.rst

@@ -126,15 +126,10 @@ Debugging hints
 -----------------------
 
 Several utilities are available that can be helpful when debugging the
-code. Not all of these will work everywhere in the code, due to possible
-conflicts in module dependencies.
+code.
 
-*debug\_ice* (**ice\_diagnostics.F90**)
-    A wrapper for *print\_state* that is easily called from numerous
-    points during the timestepping loop.
-
-*print\_state* (**ice\_diagnostics.F90**)
-    Print the ice state and forcing fields for a given grid cell.
+Namelist flags
+^^^^^^^^^^^^^^
 
 `debug\_forcing` = true (**ice\_in**)
     Print numerous diagnostic quantities associated with input forcing.
@@ -177,6 +172,19 @@ conflicts in module dependencies.
 `conserv\_check` = true (**ice\_in**)
     Diagnoses conservation in various algorithms.
 
+Subroutines
+^^^^^^^^^^^
+
+Not all of these will work everywhere in the code, due to possible
+conflicts in module dependencies.
+
+*debug\_ice* (**ice\_diagnostics.F90**)
+    A wrapper for *print\_state* that is easily called from numerous
+    points during the timestepping loop.
+
+*print\_state* (**ice\_diagnostics.F90**)
+    Print the ice state and forcing fields for a given grid cell.
+
 *global\_minval, global\_maxval, global\_sum* (**ice\_global\_reductions.F90**)
     Compute and print the minimum and maximum values for an individual
     real array, or its global sum.