Added details for osThreadJoin .. .. which causes undefined behaviour when called simultaneously from multiple threads.
Added details for osThreadJoin ..
.. which causes undefined behaviour when called
simultaneously from multiple threads.

Change-Id: I0799559312647cc2a88bd1bfce300cbd8113309a

JonatanAntoni/CMSIS_5,ARM-software/CMSIS_5,JonatanAntoni/CMSIS_5,ARM-software/CMSIS_5,ARM-software/CMSIS_5,ARM-software/CMSIS_5,JonatanAntoni/CMSIS_5,JonatanAntoni/CMSIS_5,JonatanAntoni/CMSIS_5,JonatanAntoni/CMSIS_5,ARM-software/CMSIS_5,ARM-software/CMSIS_5