Update openocd docs/configuration

[kitlith]

In general, flash via openocd -f <interface> -f tomu-flash.conf

Updated the file used for flashing the bootloader.

Doesn't overwrite openocd defaults, should fix #29 .

Documentation was updated, though it should probably be rewritten/changed a bit more in the future.

Someone who is more familiar with openocd should probably look at this to make sure that it's sane.

[kitlith]

cc @jadeaffenjaeger (since I basicly removed the configs created in #24 and did it differently)

[xobs]

Thanks for the PR!