docs: explain how to use custom configs and plugins

README.md

@@ -65,4 +65,36 @@ This is a [`Docker` action](https://github.com/actions/toolkit/blob/e2adf403d6d1
 - [conventional-changelog-lint-config-canonical](https://github.com/gajus/conventional-changelog-lint-config-canonical)
 - [commitlint-config-jira](https://github.com/Gherciu/commitlint-jira)
 
-If you have a custom shared config that lies in a private registry, let us know! We will be happy to cover this case if necessary.
+Apart from the shared configurations that are included by default, you can also include extra dependencies for other configs and plugins that you want to use.
+
+In order to do so, you can use `NODE_PATH` env var to make the action take those dependencies into account. Below is an example workflow that does that.
+
+```yaml
+name: Commitlint
+on: [pull_request]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    env:
+      GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-node@v1
+        with:
+          node-version: '10.x'
+      - run: npm install
+      - name: Add dependencies for commitlint action
+        # $GITHUB_WORKSPACE is the path to your repository
+        run: echo "::set-env name=NODE_PATH::$GITHUB_WORKSPACE/node_modules"
+      # Now the commitlint action will run considering its own dependencies and yours as well 🚀
+      - uses: wagoid/commitlint-github-action@v1
+```
+
+---
+
+💡 You can see other ways to install your dependencies (including private ones) in [the Setup Node action's docs](https://github.com/actions/setup-node).
+
+---