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/board/hisilicon/hikey/MAINTAINERS b/board/hisilicon/hikey/MAINTAINERS
index 11088ee..1045abe 100644
--- a/board/hisilicon/hikey/MAINTAINERS
+++ b/board/hisilicon/hikey/MAINTAINERS
@@ -2,5 +2,6 @@
 M:     Peter Griffin <peter.griffin@linaro.org>
 S:     Maintained
 F:     board/hisilicon/hikey
+F:     doc/board/hisilicon/hikey.rst
 F:     include/configs/hikey.h
 F:     configs/hikey_defconfig