Add more info how to manager 3rd party assets (phoenixframework#6256)

Author: ponychicken

guides/asset_management.md

@@ -26,6 +26,18 @@ If you want to import JavaScript dependencies, you have at least three options t
    import topbar from "topbar"
    ```
 
+   To ensure that `npm install` is being run when checking out your project, or when building a release add a `"cmd --cd assets npm ci"` step in `mix.exs` to the `assets.deploy` and  `assets.build` steps:
+
+```elixir   
+      "assets.build": ["cmd --cd assets npm ci", "tailwind your_app", "esbuild your_app"],
+      "assets.deploy": [
+        "cmd --cd assets npm ci",
+        "tailwind your_app --minify",
+        "esbuild your_app --minify",
+        "phx.digest"
+      ]
+```
+
 3. Use Mix to track the dependency from a source repository:
 
    ```elixir
@@ -77,6 +89,15 @@ args: ~w(js/app.js --bundle --target=es2022 --outdir=../priv/static/assets/js --
 
 If you need to reference other directories, you need to update the arguments above accordingly. Note running `mix phx.digest` will create digested files for all of the assets in `priv/static`, so your images and fonts are still cache-busted.
 
+### Ensuring fonts and images from third-party libraries are loaded
+
+If you import a Node package that depends on additional fonts or images, you might find them to fail to load. This is because they are referenced in the JS or CSS but by default Esbuild will not touch or process referenced files. You can add arguments to esbuild in `config/config.exs` to ensure that the referenced resources are copied to the output folder. The following example would copy all referenced font files to the output folder and prefix the paths with `/assets/`:
+
+```elixir
+args: ~w(js/app.js --bundle --target=es2017 --outdir=../priv/static/assets --external:/fonts/* --external:/images/* --public-path=/assets/ --loader:.woff=copy  --loader:.ttf=copy --loader:.eot=copy --loader:.woff2=copy),
+```
+For more information, see [the esbuild documentation](https://esbuild.github.io/content-types/#copy).
+
 ## Esbuild plugins
 
 Phoenix's default configuration of `esbuild` (via the Elixir wrapper) does not allow you to use [esbuild plugins](https://esbuild.github.io/plugins/). If you want to use an esbuild plugin, for example to compile SASS files to CSS, you can replace the default build system with a custom build script.