chore: rebrand Nix to Lix when it makes sense

Here's my guide so far:

$ rg '((?!(recursive).*) Nix
(?!(daemon|store|expression|Rocks!|Packages|language|derivation|archive|account|user|sandbox|flake).*))'
-g '!doc/' --pcre2

All items from this query have been tackled. For the documentation side:
that's for https://git.lix.systems/lix-project/lix/issues/162.

Additionally, all remaining references to github.com/NixOS/nix which
were not relevant were also replaced.

Fixes: https://git.lix.systems/lix-project/lix/issues/148.
Fixes: https://git.lix.systems/lix-project/lix/issues/162.
Change-Id: Ib3451fae5cb8ab8cd9ac9e4e4551284ee6794545
Signed-off-by: Raito Bezarius <raito@lix.systems>

src/nix/develop.md

@@ -77,7 +77,7 @@ R""(
 # Description
 
 `nix develop` starts a `bash` shell that provides an interactive build
-environment nearly identical to what Nix would use to build
+environment nearly identical to what Lix would use to build
 [*installable*](./nix.md#installables). Inside this shell, environment variables and shell
 functions are set up so that you can interactively and incrementally
 build your package.