When attempting to follow the docs on the installer, this error comes
up:
```
$ clan flash --flake git+https://git.clan.lol/clan/clan-core \
--ssh-pubkey ~/.ssh/id_ed25519.pub \
--keymap us \
--language en_US.utf-8 \
--dry-run flash-installer
ERROR: Language 'en_US.utf-8' is not a valid language. Run 'clan flash --list-languages' to see a list of possible languages.
```
I only decided to clean up the docs, but I'm also okay with just
downcasing the locales in `list_possible_languages()`.
- add index pages for each reference documentation category
- move concepts pages into the reference hierarchy
- render clanModules overview page in the style of the CLI overview
This reverts commit 18b64f2d0b.
The old configuration cannot be updated like this:
eve] error:
[eve] … while calling the 'head' builtin
[eve] at /nix/store/5b0hl2dnvr1sawqlkwmsnaiyqz00d34h-source/lib/attrsets.nix:1575:11:
[eve] 1574| || pred here (elemAt values 1) (head values) then
[eve] 1575| head values
[eve] | ^
[eve] 1576| else
[eve]
[eve] … while evaluating the attribute 'value'
[eve] at /nix/store/5b0hl2dnvr1sawqlkwmsnaiyqz00d34h-source/lib/modules.nix:809:9:
[eve] 808| in warnDeprecation opt //
[eve] 809| { value = builtins.addErrorContext "while evaluating the option `${showOption loc}':" value;
[eve] | ^
[eve] 810| inherit (res.defsFinal') highestPrio;
[eve]
[eve] … while evaluating the option `system.build.toplevel':
[eve]
[eve] … while evaluating definitions from `/nix/store/5b0hl2dnvr1sawqlkwmsnaiyqz00d34h-source/nixos/modules/system/activation/top-level.nix':
[eve]
[eve] … while evaluating the option `assertions':
[eve]
[eve] … while evaluating definitions from `/nix/store/5b0hl2dnvr1sawqlkwmsnaiyqz00d34h-source/nixos/modules/system/boot/systemd.nix':
[eve]
[eve] … while evaluating the option `systemd.services':
[eve]
[eve] … while evaluating definitions from `/nix/store/kpzcdgndym0qm1w490mjvk9c2qmz03h5-source/nixosModules/clanCore/zerotier':
[eve]
[eve] … while evaluating the option `clan.core.networking.zerotier.networkId':
[eve]
[eve] (stack trace truncated; use '--show-trace' to show the full, detailed trace)
[eve]
[eve] error: A definition for option `clan.core.networking.zerotier.networkId' is not of type `null or string'. Definition values:
[eve] - In `/nix/store/kpzcdgndym0qm1w490mjvk9c2qmz03h5-source/nixosModules/clanCore/networking.nix':
[eve] {
[eve] _type = "override";
[eve] content = "267efd4a15b69623";
[eve] priorit
