Switch URLs to source.puri.sm

See merge request Librem5/developer.puri.sm!9

code.puri.sm is no more

Name chapter "Development Boards"

See merge request Librem5/developer.puri.sm!8

Adding link to HowTo page

Added page with details on how to contact us with questions

Boards might be a bit terse

There were several differen spellings. I went for i.MX6 and i.MX8
(with no space in front of the number)

Condensed dev kit pages into one and added intro paragraphs on board types

See merge request Librem5/developer.puri.sm!6

Updating code repos link to point to source.puri.sm

See merge request Librem5/developer.puri.sm!4

Adding location for various board setups and full imx6 instructions based on internal wiki

See merge request Librem5/developer.puri.sm!1

Updating code repo location and fixing a title

See merge request Librem5/developer.puri.sm!3

The designers will come up with concrete examples in the future.

now that we moved away from wlroots-hacks

* use headlines
* add to index
* use https

Adding additional .. index:: entries in the document is left as
an exercise to the reader.

The files are not the master file and the toctree directive should
better not be used in these.