simplelink_lpf3: Add README.md

Detail how this directory was generated and how someone can update
to a newer SDK. Also add details on what upstream SDK version these
sources were generated.

Signed-off-by: Vebjorn Myklebust <[email protected]>
Signed-off-by: Julien Panis <[email protected]>

Author: jpanisbl

simplelink_lpf3/README.md

@@ -0,0 +1,23 @@
+# Simplelink LPF3
+
+This folder contains the low-level support required from the
+Simplelink LPF3 SDK.
+
+### Version
+
+The current version of simplelink_lpf3 is based on
+[Simplelink LPF3 8.20.00](https://www.ti.com/tool/download/SIMPLELINK-LOWPOWER-F3-SDK/).
+
+Specifically, the following components have been used:
+- Core SDK 8.10.01.04
+- RCL 8.20.01.04
+
+## Contents
+
+The folder-structure herein reflects the folder-structure in the
+Simplelink SDK. All files required to support Zephyr have been copied
+manually from the Simplelink SDK, with the exception of DPL files under
+`kernel/zephyr/dpl`, which are original and maintained in this repository.
+
+When updating to a new SDK, a comparison of the files in the 'devices'
+and 'drivers' directories should be performed to pick up any new changes.