Since Kakoune has moved to libera, it doesn't make sense for the pages to link to or mention freenode - I've updated them to point to and mention libera / its webchat instead.
Change the 'Documentation' links to match the URL pattern of the 'Get Started' links
(and of the 'Try Kakoune!' button in the homepage).
Also add the missing icon for the 'Get Started' link in the gallery.html page.
This commit adds a page to the navigation bar that will list
repositories on Github that have the "kakoune" topic set. The order
of the repositories is decided by Github (stars), and an attacker
could have their rogue plugin listed on the page, therefore users
are warned to use the plugins at their own risks.
