Update FAQ.md

FAQ.md

@@ -9,6 +9,27 @@ Usage
 
     Enthalpy and entropy are only equivalent to within an additive constant, so you should always compare enthalpy and entropy *differences* rather than enthalpy and entropy values
     
+2. My calls to REFPROP fail with a mysterious `Segementation Fault`: 
+
+    Make sure that you have at least REFPROP version 9.1 installed. If you have a license for 9.0, 
+    the upgrade is for free: http://www.nist.gov/srd/nist23.cfm
+    
+3. Transport properties
+  1. Fluid XY does not have viscosity/thermal conductivity/ ... 
+
+    Please have a look at 
+    http://www.coolprop.org/fluid_properties/PurePseudoPure.html#list-of-fluids 
+    if there is no reference for your property, we do not have the information required to 
+    implement the functionality. If you file an issue, please provide information and 
+    a link to a publication with the required data. 
+    
+  1. ..but it used to work in an earlier version of CoolProp
+    
+    For some fluids, version 5 does not have transport properties even though version 4 had 
+    that information. We decided to remove some correlations, which had very large uncertainties 
+    and we would like to make the user aware of the fact that the old implementation was 
+    experimental and results were not reliable at all.
+    
 Compilation
 -----------
 
@@ -33,4 +54,4 @@ Compilation
     sudo apt-get install g++
     ```
     
-    
+