📓 update readme

Author: Platane

README.md

@@ -35,7 +35,7 @@ Available as github action. It can automatically generate a new image each day.
 **github action**
 
 ```yaml
-- uses: Platane/snk@v2
+- uses: Platane/snk@v3
   with:
     # github user name to read the contribution graph from (**required**)
     # using action context var `github.repository_owner` or specified user
@@ -54,6 +54,10 @@ Available as github action. It can automatically generate a new image each day.
       dist/github-snake.svg
       dist/github-snake-dark.svg?palette=github-dark
       dist/ocean.gif?color_snake=orange&color_dots=#bfd6f6,#8dbdff,#64a1f4,#4b91f1,#3c7dd9
+
+    env:
+      # a github token is required to fetch the contribution calendar from github API
+      GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 ```
 
 [example with cron job](https://github.com/Platane/Platane/blob/master/.github/workflows/main.yml#L24-L29)