doc: Link to some useful talks

Talks are a great way to learn about U-Boot and have been lost now that
the Denx Wiki has gone away.

These are stored at elinux.org so link to that .

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Sean Anderson <seanga2@gmail.com>
diff --git a/doc/learn/index.rst b/doc/learn/index.rst
new file mode 100644
index 0000000..8075c01
--- /dev/null
+++ b/doc/learn/index.rst
@@ -0,0 +1,9 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Learn about U-Boot
+==================
+
+.. toctree::
+   :maxdepth: 1
+
+   talks