dts: readme: use rst extension

File content is written in rst, not markdown.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>
GitOrigin-RevId: e31e840271efc9939c8650598e169aa314208bdd
Change-Id: I02d4dc4b2c1b3d5a2aaab465a9bec106b8d12068
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/hal_stm32/+/3626236
Tested-by: CopyBot Service Account <copybot.service@gmail.com>
Commit-Queue: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
Tested-by: Jack Rosenthal <jrosenth@chromium.org>
4 files changed