message: Minor updates to CMSIS-NN documentation
diff: <!-- mdformat off(b/169948621#comment2) -->
  # Info
  +CMSIS-NN is a library containing kernel optimizations for Arm(R) Cortex(TM)-M
  +processors. To use CMSIS-NN optimized kernels instead of reference kernels, add
  +`OPTIMIZED_KERNEL_DIR=cmsis_nn` to the make command line. See examples below.
  -To use CMSIS-NN optimized kernels instead of reference kernel add
  -OPTIMIZED_KERNEL_DIR=cmsis_nn to the make line. Some micro architectures have
  -optimizations (M4 or higher), others don't. The kernels that doesn't have
  -optimization for a certain micro architecture fallback to use TFLu reference
  -kernels.
  -
  -The optimizations are almost exclusively made for int8 (symmetric) model. For
  -more details, please read
  -[CMSIS-NN doc](https://github.com/ARM-software/CMSIS_5/blob/develop/CMSIS/NN/README.md)
  +For more information about the optimizations, check out
  +[CMSIS-NN documentation](https://github.com/ARM-software/CMSIS_5/blob/develop/CMSIS/NN/README.md)
  # Example 1
  