Add test-related imports to the canonical import order listing.

PythonStyleGuide.wiki

diff --git a/PythonStyleGuide.wiki b/PythonStyleGuide.wiki
index cdda8b6..1d18a16 100644
--- a/PythonStyleGuide.wiki
+++ b/PythonStyleGuide.wiki
@@ -195,6 +195,7 @@
  * SoC framework imports
  * SoC-based module imports
  * application specific imports
+ * imports from "tests/" - test utilities and Melange-specific test modules
 
 Sorting should be done alphabetically.