docs: restore some tutorial content (#721)

Author: cotes2020

_posts/2019-08-09-getting-started.md

@@ -109,6 +109,12 @@ Now you can choose ONE of the following methods to deploy your Jekyll site.
 
 Ensure your Jekyll site has the file `.github/workflows/pages-deploy.yml`{: .filepath}. Otherwise, create a new one and fill in the contents of the [sample file][workflow], and the value of the `on.push.branches` should be the same as your repo's default branch name. And then rename your repository to `<GH_USERNAME>.github.io` on GitHub.
 
+Furthermore, if you have committed `Gemfile.lock`{: .filepath} to the repository and your local machine is not Linux, go the the root directory of your site and update the platform list:
+
+```console
+$ bundle lock --add-platform x86_64-linux
+```
+
 Now publish your Jekyll site:
 
 1. Browse to your repository on GitHub. Select the tab _Settings_, then click _Pages_ in the left navigation bar. Then, in the **Source** section (under _Build and deployment_), select [**GitHub Actions**][pages-workflow-src] from the dropdown menu.