btrfs-progs: docs: say where to get help

- The IRC channel
- The mailling list
- The btrfs-progs repo for user space bugs

Signed-off-by: Colin Snover <csnover@users.noreply.github.com>
[ Add an SoB line ]
Signed-off-by: Qu Wenruo <wqu@suse.com>

Author: csnover

Documentation/index.rst

@@ -91,6 +91,11 @@ is in the :doc:`manual pages<man-index>`.
 
    </td></tr></table>
 
+Need help?
+----------
+
+Assistance is available from the `#btrfs channel on Libera Chat <https://web.libera.chat/#btrfs>`_ or the `linux-btrfs mailing list <https://subspace.kernel.org/vger.kernel.org.html>`_. Issues with the userspace btrfs tools can be reported to the `btrfs-progs issue tracker on GitHub <https://github.com/kdave/btrfs-progs/issues>`_.
+
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