README: Do not open issues/PRs

Author: gollux

README

@@ -1,6 +1,8 @@
 This repository contains the history of the pci.ids file, which is
 automatically generated from the PCI ID Database at http://pci-ids.ucw.cz/.
 
+*Please do not open issues nor pull requests in this project.*
+
 The contents of the database and the generated files can be distributed under
 the terms of either the GNU General Public License (version 2 or later) or of
 the 3-clause BSD License.