Merge branch 'feature/openocd_doc' into 'master'

Add openocd documentation and config file

As we (=Ivan/Angus) discussed, the esp32-specific openocd/gdb documentation and helper tools will live in the esp-idf repository. This is an initial document detailing the basics of setting up OpenOCD with an esp32 module. It should be sufficient for people already familiar with a similar setup on another platform to start using JTAG for debugging. It can be expanded much more (e.g. the tracetool still is missing) but we'llhave to add that later.

See merge request !31