Gentler donation language.

Author: mdboom

doc/_templates/index.html

@@ -144,7 +144,8 @@ <h1>Toolkits</h1>
 
   <h1>Open source</h1>
 
-<p>Please <a href="http://sourceforge.net/project/project_donations.php?group_id=80706">donate</a>
+<p>Please
+consider <a href="http://sourceforge.net/project/project_donations.php?group_id=80706">donating</a>
 to support matplotlib development.</p>
 
 <p>The matplotlib <a href="{{ pathto('users/license') }}">license</a>