Document using PETSc's option -fp_trap for debugging

doc/sphinx/contributing/development-workflow.rst

@@ -182,6 +182,18 @@ errors are often caused by these). Consider using Valgrind_ to detect them.
    Your code will run much, much slower when using Valgrind, so it is important to find
    a small test case reproducing the error.
 
+Floating point exceptions
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Run PISM like this
+
+.. code-block:: bash
+
+   pismr -fp_trap -on_error_attach_debugger [other options]
+
+to catch floating point exceptions (division by zero, operations with a not-a-number or
+infinity, square root of a negative number, etc).
+
 Issues visible in parallel runs only
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~