chore: Add linters section to guide

apps/core/guides/features/linters.md

@@ -0,0 +1,31 @@
+# Linters
+
+Legendary ships with a set of reasonable default linter configurations to help
+enforce consistent code style in your application. This is particularly valuable
+when working together as a team. However, even when working solo, linters will
+find some errors in your code and help you to avoid needless changes in the future.
+
+Included linters:
+
+- *credo* for Elixir
+- *prettier* for JavaScript
+- *stylelint* for CSS
+
+## Pre-commit hooks
+
+If you would like to lint your code before every commit, you can use
+[lefthook](https://github.com/evilmartians/lefthook) to do so. We include a
+lefthook.yml that runs credo, prettier, and stylelint for you.
+
+First, if you do not have it installed already, you will need to
+[install lefthook](https://github.com/evilmartians/lefthook/blob/master/docs/other.md#installation).
+On the Mac with Homebrew, this is as simple as `brew install lefthook`. Instructions
+for other environments are available in the lefthook documentation linked above.
+
+Then you can install the hooks via `lefthook install`. You can test them without
+committing by running `lefthook run pre-commit`.
+
+## Linters in CI
+
+The included `.gitlab-ci.yml` runs credo, prettier, and stylelint in CI as an
+additional consistency check.

apps/core/mix.exs

@@ -61,6 +61,7 @@ defmodule Legendary.Core.MixProject do
       "guides/features/feature-flags.md",
       "guides/features/i18n.md",
       "guides/features/tasks-and-scripts.md",
+      "guides/features/linters.md",
     ]
   end