fix to app-specific info

Author: curfman

README.md

@@ -60,16 +60,20 @@ as well as the following commonly needed external packages
 
 ##Application-Specific Installs
 
-The xSDK includes the
-[Alquimia](https://github.com/LBL-EESA/alquimia-dev) geochemistry package, which in turn uses the
-[PFlotran](http://www.pflotran.org) chemistry engine.  The script can install these application-specific packages, as well as other external packages needed by the 
+Work in the xSDK is motivated by large-scale scientific applications, including use-cases in 
+environmental system science.  The xSDK includes the
+[Alquimia](https://github.com/LBL-EESA/alquimia-dev) geochemistry package, which in turn uses 
+[PFlotran](http://www.pflotran.org) as a chemistry engine.  The script can install these 
+application-specific packages, as indicated below.  The script can also install 
+external packages that are needed by the
 [Amanzi](https://software.lanl.gov/ascem/amanzi) application.
 
+
 ## Options for Application-Specific Installs
 
-    --download-alquimia  --download-pflotran    Install Alquimia and PFlotran chemistry engine.
+    --download-alquimia  --download-pflotran    Install Alquimia and PFlotran.
 
-    --download-ideas   Install external software as needed by the Amanzi application.
+    --download-ideas   Install xSDK packages and external software needed by Amanzi.
 
 
 ##Notes