doc: add HiSilicon board documentation to HTML docs

Add the README files for the HiSilicon boards to the HTML documentation.
This required a bit of reformatting.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/board/hisilicon/index.rst b/doc/board/hisilicon/index.rst
new file mode 100644
index 0000000..5455b76
--- /dev/null
+++ b/doc/board/hisilicon/index.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+HiSilicon
+=========
+
+.. toctree::
+   :maxdepth: 2
+
+   hikey
+   hikey960
+   poplar