Add comprehensive documentation for bun ci command (#21231)

Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>

docs/cli/install.md

@@ -245,7 +245,8 @@ linker = "hoisted"
 
 ## CI/CD
 
-Looking to speed up your CI? Use the official [`oven-sh/setup-bun`](https://github.com/oven-sh/setup-bun) action to install `bun` in a GitHub Actions pipeline.
+
+Use the official [`oven-sh/setup-bun`](https://github.com/oven-sh/setup-bun) action to install `bun` in a GitHub Actions pipeline:
 
 ```yaml#.github/workflows/release.yml
 name: bun-types
@@ -264,4 +265,33 @@ jobs:
         run: bun run build
 ```
 
+For CI/CD environments that want to enforce reproducible builds, use `bun ci` to fail the build if the package.json is out of sync with the lockfile:
+
+```bash
+$ bun ci
+```
+
+This is equivalent to `bun install --frozen-lockfile`. It installs exact versions from `bun.lock` and fails if `package.json` doesn't match the lockfile. To use `bun ci` or `bun install --frozen-lockfile`, you must commit `bun.lock` to version control.
+
+And instead of running `bun install`, run `bun ci`.
+
+```yaml#.github/workflows/release.yml
+name: bun-types
+jobs:
+  build:
+    name: build-app
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+      - name: Install bun
+        uses: oven-sh/setup-bun@v2
+      - name: Install dependencies
+        run: bun ci
+      - name: Build app
+        run: bun run build
+```
+
+
+
 {% bunCLIUsage command="install" /%}