2013-04-11: Added guile stdin usage.

Added guile stdin usage.

diff --git a/Readme.txt b/Readme.txt
--- a/Readme.txt
+++ b/Readme.txt
@@ -23,3 +23,9 @@ becomes
 
 
 Usage: ./wisp.py infile.wisp > outfile.lisp
+
+More powerful usage (in case you use unix):
+
+    cat infile.wisp | ./wisp.py - | guile -s /dev/stdin
+
+That converts the infile to scheme and executes it via guile.