- inform about unusual case

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@32343 20353a03-c40f-0410-a6d1-a30d3c3de9de

buildout/bootstrap/README.txt

+bootstrap.py file is updated from time to time from:
+  http://svn.zope.org/*checkout*/zc.buildout/trunk/bootstrap/bootstrap.py
+
+There is no need to fix it locally, all changes shall go upstream.
+Moreover buildout has ability to autoupdate itself, so local manipulations on
+that file might have side effects.