Update required on pyOCD tutorial

[MarceloSalazar]

Page link

https://os.mbed.com/docs/mbed-os/development/debug-test/debug-microbit.html

Expected to find...

Generic and valid instructions on debugging with pyOCD and Mbed boards

Found

• References to Microbit and nrf51 - note these targets are not supported in Mbed 6
• References to Linux (4.1) - don't know what this is
• pyOCD (0.4.5) - latest release is v0.26.1 - see https://github.com/mbedmicro/pyOCD/releases
• gcc version is old: arm-none-eabi-gdb (7.9.1) and we're pointing a not official location: https://launchpad.net/gcc-arm-embedded

Note the pyOCD is very useful and we should keep this tutorial!

[ciarmcom]

Thank you for raising this detailed GitHub issue. I am now notifying our internal issue triagers.
Internal Jira reference: https://jira.arm.com/browse/IOTDOCS-1554