Moved older (partially obsolete) documentation to a subdirectory

README.md

@@ -2,4 +2,6 @@ vdt-docs
 ========
 
 Documentation for VDT Eclipse plugin, the latest documentation is in VDT-UserManualAddendum.pdf and in ExDT-TSL-Eng.pdf files
-Some of the information in the other files may be obsolete (coming from the original 2006 version), but most is still valid
+Some of the information in the other files may be obsolete (coming from the original 2006 version), but most is still valid.
+
+These older files are available in older_docs subdirectory.