docs(v2): add deployment workflow manual for GitHub Actions (#2670)

* docs: add deployment workflow manual for GitHub Actions

Steps to build and deploy Docusaurus with GitHub Actions

* docs(v2): improve formatting

Co-authored-by: Alexey Pyltsyn <lex61rus@gmail.com>

website/docs/deployment.md

@@ -83,6 +83,77 @@ GIT_USER=<GITHUB_USERNAME> yarn deploy
 cmd /C "set "GIT_USER=<GITHUB_USERNAME>" && yarn deploy"
 ```
 
+### Triggering deployment with GitHub Actions
+
+[GitHub Actions](https://help.github.com/en/actions) allow you to automate, customize, and execute your software development workflows right in your repository.
+
+This workflow assumes your documentation resided in `documentation` branch of your repository and your [publishing source](https://help.github.com/en/github/working-with-github-pages/configuring-a-publishing-source-for-your-github-pages-site)
+is configured for `gh-pages` branch.
+
+1. Generate a new [SSH key](https://help.github.com/en/github/authenticating-to-github/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent).
+1. By default, your public key should have been created in `~/.ssh/id_rsa.pub` or use the name you've provided in the previous step to add your key to [GitHub deploy keys](https://developer.github.com/v3/guides/managing-deploy-keys/).
+1. Copy key to clipboard with `xclip -sel clip < ~/.ssh/id_rsa.pub` and paste it as a [deploy key](https://developer.github.com/v3/guides/managing-deploy-keys/#deploy-keys ) in your repository. Copy file content if the command line doesn't work for you. Check the box for `Allow write access` before saving your deployment key.
+1. You'll need your private key as a [GitHub secret](https://help.github.com/en/actions/configuring-and-managing-workflows/creating-and-storing-encrypted-secrets) to allow Docusaurus to run the deployment for you.
+1. Copy your private key with `xclip -sel clip < ~/.ssh/id_rsa` and paste a GitHub secret with name `GH_PAGES_DEPLOY`. Copy file content if the command line doesn't work for you. Save your secret.
+1. Create you [documentation workflow file](https://help.github.com/en/actions/configuring-and-managing-workflows/configuring-a-workflow#creating-a-workflow-file) in `.github/workflows/`. In this example it's `documentation.yml`.
+
+```yaml title="documentation.yml"
+name: documentation
+
+on:
+  pull_request:
+    branches: [documentation]
+  push:
+    branches: [documentation]
+
+jobs:
+ checks:
+   if: github.event_name != 'push'
+   runs-on: ubuntu-latest
+   steps:
+     - uses: actions/checkout@v1
+     - uses: actions/setup-node@v1
+       with:
+         node-version: '12.x'
+         run: |
+          npm ci
+          npm run build
+ gh-release:
+   if: github.event_name != 'pull_request'
+   runs-on: ubuntu-latest
+   steps:
+    - uses: actions/checkout@v1
+    - uses: actions/setup-node@v1
+      with:
+        node-version: '12.x'
+    - name: Add key to allow access to repository
+      env:
+        SSH_AUTH_SOCK: /tmp/ssh_agent.sock
+      run: |
+        mkdir -p ~/.ssh
+        ssh-keyscan github.com >> ~/.ssh/known_hosts
+        echo "${{ secrets.GH_PAGES_DEPLOY }}" > ~/.ssh/id_rsa
+        chmod 600 ~/.ssh/id_rsa
+        cat <<EOT >> ~/.ssh/config
+        Host github.com
+        HostName github.com
+        IdentityFile ~/.ssh/id_rsa
+        EOT
+    - name: Release to GitHub Pages
+      env:
+        USE_SSH: true
+        GIT_USER: git
+      run: |
+        git config --global user.email "actions@gihub.com"
+        git config --global user.name "gh-actions"
+        npm ci
+        npx docusaurus deploy
+```
+
+1. Now when a new pull request arrives towards your repository in branch `documentation` it will automatically ensure that Docusaurus build is successful.
+1. When pull request is merged to `documentation` branch or someone pushes to `documentation` branch directly it will be built and deployed to `gh-pages` branch.
+1. After this step, your updated documentation will be available on the GitHub pages.
+
 ### Triggering deployment with Travis CI
 
 Continuous integration (CI) services are typically used to perform routine tasks whenever new commits are checked in to source control. These tasks can be any combination of running unit tests and integration tests, automating builds, publishing packages to NPM, and deploying changes to your website. All you need to do to automate the deployment of your website is to invoke the `yarn deploy` script whenever your website is updated. The following section covers how to do just that using [Travis CI](https://travis-ci.com/), a popular continuous integration service provider.