Add note about sourcing

doc/development/open-questions/index.mdwn

@@ -119,6 +119,9 @@ Discussion of metacognitive strategies that could have computer aides.
               everywhere). It is important to know where it occurs to avoid
               parochialism.
         + Temporal
+- Sourcing
+    * Primary source, secondary source, etc.
+        + Summaries are not the same as the primary source.
 - Thinking routines
     * <https://www.theconsortiumforpubliceducation.org/resource/project-based-learning-resources-pbl/research/>
     * <http://www.pz.harvard.edu/thinking-routines>