Errors in OpenOCD-Nuttx tutorial

About https://micro-ros.github.io/docs/tutorials/advanced/debugging_gdb_openocd/

 * "nuttx_header.h" is in "src/rtos" (not just src, as currently written)
 * missing dependencies: 
   * libftdi1-dev
   * libusb-dev
   * libusb-1.0-0-dev
   * libjaylink-dev
 * On Ubuntu 18.04. the compile will fail due to -Werror, need a workaround