Mention autopep8 in Hacking.rst

The scripts in the tools now is able to distinguish,
the autopep8 error codes better.

Change-Id: I9ea19009118ed418e3666fad45d2e0eb676204c8
diff --git a/tox.ini b/tox.ini
index 433f168..230249f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -198,7 +198,7 @@
 
 [testenv:pep8]
 deps =
-    -r test-requirements.txt
+    -r{toxinidir}/test-requirements.txt
     autopep8
 basepython = python3
 commands =
@@ -210,7 +210,7 @@
 deps = autopep8
 basepython = python3
 commands =
-    autopep8 --max-line-length=79  --experimental --in-place -r tempest setup.py
+    {toxinidir}/tools/format.sh
 
 [testenv:uuidgen]
 commands =