docs: add plugin file scoping (includes) documentation

src/content/docs/linter/plugins.mdx

@@ -30,7 +30,34 @@ the following configuration:
 ```
 
 The plugin will now be enabled on all supported files the linter runs on. You
-can see its results when running `biome lint` or `biome check`. For example:
+can see its results when running `biome lint` or `biome check`.
+
+### File Scoping
+
+By default, a plugin runs on every file the linter processes. If a plugin only
+applies to certain files, you can restrict it using `includes` glob patterns.
+Use negated globs (prefixed with `!`) for exclusions:
+
+```json name="biome.json"
+{
+    "plugins": [
+        {
+            "path": "./react-plugin.grit",
+            "includes": ["src/components/**"]
+        },
+        {
+            "path": "./ts-only-plugin.grit",
+            "includes": ["src/**/*.ts", "!**/*.test.ts"]
+        }
+    ]
+}
+```
+
+When `includes` is set, the plugin only runs on files matching at least one of
+the patterns. Negated patterns act as exceptions, following the same semantics
+as [`.gitignore`](https://git-scm.com/docs/gitignore#_pattern_format).
+
+For example:
 
 ```shell
 $ biome lint

src/content/docs/reference/configuration.mdx

@@ -50,6 +50,46 @@ This is required so Biome can orchestrate multiple files in CLI and editors at t
 
 > Default: `true`
 
+## `plugins`
+
+A list of [GritQL plugins](/linter/plugins/) to enable. Each entry can be
+either a simple path string or an object with a path and optional file-scoping
+options.
+
+Simple path:
+
+```json title="biome.json"
+{
+  "plugins": ["./my-plugin.grit"]
+}
+```
+
+Path with file scoping:
+
+```json title="biome.json"
+{
+  "plugins": [
+    {
+      "path": "./react-plugin.grit",
+      "includes": ["src/components/**", "!src/components/generated/**"]
+    }
+  ]
+}
+```
+
+You can mix both forms in the same list.
+
+### `plugins.<ITEM>.path`
+
+Path to the plugin file (`.grit`) or plugin directory containing a
+`biome-manifest.jsonc`.
+
+### `plugins.<ITEM>.includes`
+
+A list of glob patterns for files the plugin should run on. If set, only
+matching files are analyzed by this plugin. Use negated globs (prefixed with
+`!`) for exclusions, following the same semantics as
+[`.gitignore`](https://git-scm.com/docs/gitignore#_pattern_format).
 
 ## `files`