debug: clarify that symbolize.py is to be run on the host

The target usually doesn't have the tools required by symbolize.py
(Python interpreter, binutils tools...) nor the original ELF files.
This script is meant to be run on the host in the build environment.

Signed-off-by: Jerome Forissier <jerome@forissier.org>
Acked-by: Etienne Carriere <etienne.carriere@linaro.org>

debug/abort_dumps.rst

@@ -70,6 +70,8 @@ analysis of such issues. It is located in the OP-TEE OS source tree in
 ``scripts/symbolize.py`` and is also copied to the TA development kit.
 Whenever you are confronted with an error message reporting a serious error and
 containing a ``"Call stack:"`` line, you may use the symbolize script.
+It is meant to be run on the host system (build environment), not on the
+target.
 
 ``symbolize.py`` reads its input from ``stdin`` and writes extended debug
 information to ``stdout``. The ``-d`` (directories) option tells the script