Updated README for prep_syndata

prep_syndata/README_prepsyndata.txt

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- FLEXINVERT SYNTHETIC DATA PREPARATION 
+ FLEXINVERT-Plus SYNTHETIC DATA PREPARATION 
 
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@@ -9,7 +9,7 @@ Description:
 
 Notes: 
   1) Output from a forward run of FLEXINVERT (run_mode = 0) 
-     are needed before running synthetic data test.
+     are needed before running prep_syndata
   2) For CO2 only NEE fluxes are perturbed.
   3) Fluxes are returned on the same domain as the flexpart
      grid_time files (if nested is true this is the nested
@@ -17,7 +17,8 @@ Notes:
      greater domain than the flexpart files.
   4) If the inversion domain (covered by state vector) is 
      smaller than the flexpart domain, only the fluxes inside
-     the inversion domain are perturbed.
+     the inversion domain are perturbed (fluxes outside this 
+     domain are equal to the prior).
 
 Synthetic Data:
   1) Prior fluxes: prepared by randomly perturbing prior fluxes