add WG-docs-checklist to "impl Future for Rust"

As new working groups crop up, it would be nice to keep this post up to date, since it's currently the best directory of all the groups.

Author: QuietMisdreavus

_posts/2017-09-18-impl-future-for-rust.md

@@ -186,6 +186,12 @@ chat room!**
     <td><a href="https://paper.dropbox.com/doc/WG-rbe-Tgd0wu70N6zSmACkNL3TI">Learn more</a></td>
     <td><a href="https://gitter.im/rust-impl-period/WG-docs-rbe">Chat</a></td>
 </tr>
+<tr>
+    <td><b>WG-docs-checklist</b></td>
+    <td>Help finish the standard library documentation!</td>
+    <td><a href="https://paper.dropbox.com/doc/Finish-the-docs-checklist-WG-docs-checklist-7CiH332jWblQUTqUOVXaZ">Learn more</a></td>
+    <td><a href="https://gitter.im/rust-impl-period/WG-docs-checklist">Chat</a></td>
+</tr>
 </table>
 
 ### Dev tools team