ChangeLog: mention doc update

ChangeLog

@@ -85,6 +85,7 @@ Small changes:
   * Fix forcing calibration of never-calibrated archs.
   * CUDA applications are no longer compiled with the "-arch sm_13"
     option. It is specifically added to applications which need it.
+  * Documentation is not built if necessary tools are missing
 
 StarPU 1.0.3 (svn revision 7379)
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