docs: add GitLab pages CI (#549)

* add .gitlab-ci.yml

* move GitLab CI to hosting.md

* remove extra folder name

Co-authored-by: Jacky Zhao <j.zhao2k19@gmail.com>

* remove test from gitlab instructions

* run prettier

---------

Co-authored-by: Jacky Zhao <j.zhao2k19@gmail.com>

docs/hosting.md

@@ -166,3 +166,56 @@ Using `docs.example.com` is an example of a subdomain. They're a simple way of c
 3. Go to the [Vercel Dashboard](https://vercel.com/dashboard) and select your Quartz project.
 4. Go to the Settings tab and then click Domains in the sidebar
 5. Enter your subdomain into the field and press Add
+
+## GitLab Pages
+
+You can configure GitLab CI to build and deploy a Quartz 4 project.
+
+In your local Quartz, create a new file `.gitlab-ci.yaml`.
+
+```yaml title=".gitlab-ci.yaml"
+stages:
+  - build
+  - deploy
+
+variables:
+  NODE_VERSION: "18.14"
+
+build:
+  stage: build
+  rules:
+    - if: '$CI_COMMIT_REF_NAME == "v4"'
+  before_script:
+    - apt-get update -q && apt-get install -y nodejs npm
+    - npm install -g n
+    - n $NODE_VERSION
+    - hash -r
+    - npm ci
+  script:
+    - npx prettier --write .
+    - npm run check
+    - npx quartz build
+  artifacts:
+    paths:
+      - public
+  cache:
+    paths:
+      - ~/.npm/
+    key: "${CI_COMMIT_REF_SLUG}-node-${CI_COMMIT_REF_NAME}"
+  tags:
+    - docker
+
+pages:
+  stage: deploy
+  rules:
+    - if: '$CI_COMMIT_REF_NAME == "v4"'
+  script:
+    - echo "Deploying to GitLab Pages..."
+  artifacts:
+    paths:
+      - public
+```
+
+When `.gitlab-ci.yaml` is commited, GitLab will build and deploy the website as a GitLab Page. You can find the url under `Deploy` -> `Pages` in the sidebar.
+
+By default, the page is private and only visible when logged in to a GitLab account with access to the repository but can be opened in the settings under `Deploy` -> `Pages`.