* Link to concepts section fixed.
The {base} part of the link to 'Concepts' section seems to already include /doc in its path, thus directing the user to /docs/docs/... path (specifically https://www.openhab.org/docs/docs/concepts/index.html), whereas the proper link should be https://www.openhab.org/docs/concepts/.
* Update tutorials/getting_started/things_simple.md
Signed-off-by: Jerome Luckenbach <github@luckenba.ch>
Co-authored-by: Jerome Luckenbach <github@luckenba.ch>