Add list introducing features and usage.

To have a quick glimpse on how gwit may be used.
Try better wording for multiple authorship non-goal.

It regards keys signing the repo's main branch, multiple authors committing to
other branches is ok (as long as the merge commit is signed by the site key).
Move links section further up.

So that casual readers do not need to go over the rather lengthy goals
Add links to The Oldest gwit Site.

As a documentation site.
Replace site "recommendations" with "introductions".

As per spec updates.
Link to gwet client.
Link to project home page.
Links to lightning talk at BattleMesh v15.

Unfortunately, parts of the recording are missing.
Add design non-goals.
Add, define and prioritize architectural design goals.
Add forgiveness and compatibility to functional goals.
Add, define and prioritize functional design goals.
Minor changes for readability.
Add link to Git website.
Put links after text, Gemini-style, to avoid distractions.
Indicate what petnames are used for.
Initial commit (basic project intro, plus REUSE 3.0 files).