save default logo a bit bigger

git-svn-id: svn://svn.code.sf.net/p/rdkit/code/trunk@2437 a5045d30-4826-4484-9c7f-6e55a06ddc77
further updates to the install doc

git-svn-id: svn://svn.code.sf.net/p/rdkit/code/trunk@2438 a5045d30-4826-4484-9c7f-6e55a06ddc77