docs(omarchy): #78 Omarchy → Nomarchy migrant one-pager

Add docs/OMARCHY.md for users coming from Omarchy (VISION § F). Leads
with the one real difference — imperative dotfiles vs a declarative flake
built via the menu, with rollback through NixOS generations — then maps
the deltas: install (ISO/nomarchy-install or MIGRATION.md), a familiar
keybindings table, theming (SUPER+T / nomarchy-theme-sync), installing
software (home.packages / nix shell, no AUR), and update+rollback
(nomarchy-pull/-rebuild/-home, boot-menu generations, nomarchy-doctor).
Registered in docs/README.md; VISION § F marked shipped.

The Nomarchy side is grounded in the code: keybindings pulled from
keybinds.nix, and every cited command (7), the nsearch alias, and the
named theme slugs (gruvbox/rose-pine/nord) verified to exist. Omarchy-side
claims kept to known facts (Arch, dotfiles, pacman/AUR).

Verification: V0 (docs-only); commands/slugs/binds checked against the tree.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/README.md

@@ -13,6 +13,7 @@ tree for the same facts.
 | [RECOVERY.md](RECOVERY.md) | Users | Broken theme/desktop/boot → undo |
 | [OVERRIDES.md](OVERRIDES.md) | Users | Downstream Nix overrides |
 | [MIGRATION.md](MIGRATION.md) | Users | Existing NixOS → Nomarchy without reinstall |
+| [OMARCHY.md](OMARCHY.md) | Users | Coming from Omarchy — bindings/theme/install/config map |
 
 ## Related (not under `docs/`)