Put install.md first in the docs navigation

It is the page people need before any of the others, and without an entry in
the order and description maps it would have sorted to the end unlabelled.

Author: ralyodio

apps/web/lib/docs.ts

@@ -15,6 +15,7 @@ export type DocMeta = { slug: string; title: string; description: string }
 
 /** Ordered so the sidebar reads as a path through the product, not alphabetically. */
 const ORDER = [
+  'install',
   'getting-started',
   'defaults',
   'cli',
@@ -29,6 +30,7 @@ const ORDER = [
 ]
 
 const DESCRIPTIONS: Record<string, string> = {
+  install: 'The one-line installer, what it decides, and how to remove it.',
   'getting-started': 'From an empty config to a working transfer.',
   defaults: 'What DiskPush does when you tell it nothing, and why.',
   cli: 'The full command grammar, options and exit codes.',