Rules: add fundraising/donation rule (TheOdinProject#3643)

Because
We've decided to blanket ban fundraising/donation initiatives on the
server.

This PR
- Adds a rule covering fundraising and donation links.

app/views/static_pages/community_rules.html.erb

@@ -55,6 +55,9 @@
       <li>
         <strong>Crossposting or Duplicate Posts</strong> by posting the same message to different channels or asking for help in multiple channels at once. You should allow at least <strong>30 minutes</strong> for a reply. While you are waiting, make sure that you posted in the most relevant channel, provided a <a href="/how_to_ask" target="_blank">detailed question</a>, and continue trouble-shooting. It is recommended to edit your post with the results of things you have tried. If your post gets buried, you may repost your question, otherwise, you may direct people to your question in a more active channel.
       </li>
+      <li>
+        <strong>No fundraising or donation drives</strong> while we're very sympathetic to variety of causes, moderating the authenticity of such initiatives is not something we can commit to. Please find other communities that allow such activities, including sharing links to this kind of content.
+      </li>
     </ul>
 
     <h3 id="zap-level-1">1 Zap - Warning for Minor Violations</h3>