add new diagrams and update docs

I added the new diagrams and updated the docs to include them along with
an explanation of what's going on for the simpler overview.

I included the graphml files so they can be imported and edited/improve
later on but I don't know how they'll work in other programs; I created
them in yEd: yworks.com/products/yed

The dark diagrams have transparent backgrounds so they should be
suitable for any shade and the light diagrams are simply white. SVGs are
including for editing colors and exporting at various sizes.
move wisteria guide to separate doc
replace wisteria guide with one for sprig
make spec links relative

The previous links would lead to sourcehut's root and 404 but these should
lead to the correct locations.
Remove outdated implementation links.
docs: fix link to node encoding
docs: clarify node ID encoding and example
docs: define how to encode node IDs as strings
add missing word and use better link descriptor
normalize capitalization and correct spelling
normalize capitalization and link to twig
correct capitalization
replace "here" link text with better descriptors

Same as 8a82515
grammatical, spelling, and capitalisation changes

I corrected a few misspelled words, capitalised the first letter
of bullets and the words "Arbor" and "Forest" in a couple of
places, and added backticks around the sprout:// protocol string.
improve clarity for sending replies

The process for sending a reply was somewhat ambiguous before, assuming
the user would know what to do based on the UI itself.
reword extraction phrase and remove newline

Double-clicking doesn't always extract the archive in the current
directory so it would be better to specify that that's *generally*
how it can be done.

I also remove an extra newline.
reword installation phrase

In general, it's better to refrain from using "here" as link text for
web accessibility. Descriptive links that indicate the destination are
chore: dummy commit to refresh docs
doc: update biweekly meeting info
doc: simplify getting started and add update steps