Added "doc" target to match the other document-prefix targets.
diff --git a/Doc/html/Makefile b/Doc/html/Makefile
index 4ff1dd3..8bbb691 100644
--- a/Doc/html/Makefile
+++ b/Doc/html/Makefile
@@ -45,6 +45,7 @@
 .PHONY: api ext lib mac ref tut
 
 api: api/api.html
+doc: doc/doc.html
 ext: ext/ext.html
 lib: lib/lib.html
 mac: mac/mac.html