README: Add an intro section and lib section

Add intro section explaining basics of the package.
Also add few words on the lib folder.

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>
1 file changed
tree: aec16067402e7d41cd684536d5788787cbf0ab08
  1. CMakeLists.txt
  2. README
  3. lib/
  4. stm32cube/
  5. zephyr/