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>