Add rst2html variable.

docs/tutorial/Makefile

@@ -1,9 +1,10 @@
+RST2HTML = rst2html
 TXT=$(shell ls *.txt)
 
 ALL: index.html
 
 index.html: $(TXT)
-	rst2html.py index.txt index.html
+	$(RST2HTML) index.txt index.html
 
 clean:
 	rm -f index.html