Update to latest bootstrap.py

Downloaded from https://bootstrap.pypa.io/bootstrap-buildout.py
Remove find-links

First of all, all of zope.* is on PyPI, second, HTTP is not secure.
Restore README.txt from Subversion

I think it was lost in the svn-to-git conversion.

Restoration:

  svn co svn://svn.zope.org/repos/main/zc.relation/trunk zc.relation
  cd zc.relation
  svn log
  svn up -r 127872
  cp README.rst ...
MANIFEST.in and .gitignore gardening