add docs

README.md

@@ -123,6 +123,10 @@ Custom [unjs/jiti](https://github.com/unjs/jiti) instance used to import configu
 
 Custom [unjs/jiti](https://github.com/unjs/jiti) options to import configuration files.
 
+### `giget`
+
+Options passed to [unjs/giget](https://github.com/unjs/giget) when extending layer from git source.
+
 ### `envName`
 
 Environment name used for [environment specific configuration](#environment-specific-configuration).
@@ -205,6 +209,39 @@ Layers:
 ]
 ```
 
+## Extending Config Layer from Remote Sources
+
+You can also extend configuration from remote sources such as npm or github.
+
+In the repo, there should be a `config.ts` (or `config.{name}.ts`) file to be considered as a valid config layer.
+
+**Example:** Extend from a github repository
+
+```js
+// config.ts
+export default {
+  extends: "gh:repo/owner",
+};
+```
+
+**Example:** Extend from a github repository with branch and subpath
+
+```js
+// config.ts
+export default {
+  extends: "gh:repo/owner/test/fixture/_github#main",
+};
+```
+
+**Example:** Extend with custom configuration ([giget](https://github.com/unjs/giget) options)
+
+```js
+// config.ts
+export default {
+  extends: ["gh:repo/owner", { giget: { auth: process.env.GITHUB_TOKEN } }],
+};
+```
+
 ## Environment-specific configuration
 
 Users can define environment-specific configuration using these config keys: