added note about creating stacktraces

doc/intern.txt

@@ -149,6 +149,9 @@ To create a new compiler for each run, use ``koch temp``::
 
   ./koch temp c /tmp/test.nim
 
+``koch temp`` creates a debug build of the compiler, which is useful
+to create stacktraces for compiler debugging.
+
 ``koch temp`` returns 125 as the exit code in case the compiler
 compilation fails. This exit code tells ``git bisect`` to skip the
 current commit.::