Fix some minor language and formatting issues.
Copy info about the non-functioning display to Known Issues.

Some more hardware details

See merge request Librem5/developer.puri.sm!105

devkit: List picocom --quiet instead of -q

See merge request Librem5/developer.puri.sm!111

Community member says Ubuntu doesn't do -q

Fix note directive

See merge request Librem5/developer.puri.sm!110

README: Indicate build status

See merge request Librem5/developer.puri.sm!109

Now that we pulish the docs on commit the build status is even more
important.

Start fleshing out hardware reference information

See merge request Librem5/developer.puri.sm!108

Application Development chapter refactor

See merge request Librem5/developer.puri.sm!102

Move the Design section into the App Development Guides.
Add placeholder guides.
Tidy up the GNOME documentation.

Add a Guides section.
Move the Flatpak setup information up a level.

Prepare to move parts to sections on packaging and publishing.

Devkit handholding 2

See merge request Librem5/developer.puri.sm!103

Update hardware information

See merge request Librem5/developer.puri.sm!104

DON'T PANIC