[L] Change in flashrom[main]: doc: Convert serprog docs to rst and add to doc directory

[J. Neuschäfer (Code Review)]

Attention is currently required from: Anastasia Klimchuk, Riku Viitanen, Swift Geek (Sebastian Grzywna), Sydney, Thomas Heijligen, Urja Rannikko.

J. Neuschäfer has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/82018?usp=email )

Change subject: doc: Convert serprog docs to rst and add to doc directory
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Patch Set 2:

(1 comment)

File doc/supported_hw/supported_prog/serprog/overview.rst:

https://review.coreboot.org/c/flashrom/+/82018/comment/8c19d37d_aa0b4ff7 :
PS1, Line 83: See `the github page <https://github.com/dword1511/serprog-stm32vcp#serprog-stm32vcp>`_ for further details, source code etc.
Somewhat. But I'd shift the focus on the firmware, because stm32-vserprog is not just a specific piece of hardware, but a firmware that runs on different hardware.

Additionally, I always find superlative claims ("the most powerful") a bit dubious, even though STM32s are certainly a good option.

Something like this:
> A powerful option is `stm32-vserprog <https://github.com/dword1511/stm32-vserprog/>`_, a firmware for various STM32-based boards that turns them into serprog-based programmers with SPI clock speeds up to 36 MHz.