Fix v0.5.2.rst whatsnew text (#456)

Restoring text that was deleted by mistake

Author: cwhanse

docs/sphinx/source/whatsnew/v0.5.2.rst

@@ -1,4 +1,4 @@
-0.. _whatsnew_0520:
+.. _whatsnew_0520:
 
 v0.5.2 (__, 2017)
 -------------------------
@@ -12,10 +12,12 @@ API Changes
 
 Enhancements
 ~~~~~~~~~~~~
+* Improve clearsky.lookup_linke_turbidity speed, changing .mat source file
+  to .h5 (:issue:`437`)
 * Updated libraries for CEC module parameters to SAM release 2017.9.5 
-(library dated 2017.6.30) and CEC inverter parameters to file posted to 
-www.github.com/NREL/SAM on 2018.3.18, with one entry removed due to a 
-missing parameter value. (:issue:'440')
+  (library dated 2017.6.30) and CEC inverter parameters to file posted to 
+  www.github.com/NREL/SAM on 2018.3.18, with one entry removed due to a 
+  missing parameter value. (:issue:'440')
 
 Bug fixes
 ~~~~~~~~~