Update install instructions

README.md

@@ -50,6 +50,27 @@ at Madison. Development began in 2023.
       For instance stop following the install instructions when
       the discussion gets to SPARTA+
 
+  - Make sure the ShiftX2 code is accessible in the path:
+  
+      In the ShiftX2 install instructions you visited there is discussion
+      in place to put these lines of code:
+      
+        export SHIFTX2_DIR=~/Programs/shiftx2-linux
+        export PATH=$PATH:$SHIFTX2_DIR
+
+      in your ~/.bashrc file or in your ~/.profile file.
+      
+      However that assumes you will be running ShiftX2 via the Bash shell.
+      But nmrPipe uses the C-shell. So you should also make the following
+      equivalent changes to your ~/.cshrc file:
+      
+        setenv SHIFTX2_DIR ~/Programs/shiftx2-linux
+        setenv PATH ${PATH}:${SHIFTX2_DIR}
+
+      Please note that in both cases if you installed shiftx2-linux in
+      someplace other than ~/Programs then you should make the same path
+      change to these file edit examples above.
+      
   - Install BPHON in ChimeraX
 
       Start up ChimeraX from a csh or tcsh terminal shell. This is necessary