Briefly give examples of benefit to WL of WFIRST overlap

(LSSTScienceCollaborations#630)

whitepaper/Cosmology/wl.tex

@@ -426,7 +426,10 @@ \subsection{Deep vs Wide}
 of LSST science drivers, including Bayesian analyses.  By the same reasoning, it
 would be important to cover a significant area [perhaps 2000 sq. deg] to full
 depth during the first year of the survey.  This would allow full assessment of
-systematics, and could be chosen to overlap the WFIRST footprint.
+systematics, and could be chosen to overlap the WFIRST footprint.  Such an
+overlap may enable additional systematics checks of photometric redshift accuracy
+(exploiting WFIRST infrared photometry) and the impact of blends (exploiting the
+smaller WFIRST PSF).
 
 Metrics for reaching the SRD goals for WL related science are needed. Long
 before LSST is on the sky such metrics can be applied to realistic simulations