docs: add note about CircleCI config (#1141)

Author: andrewvasilchuk

docs/guides-ci-setup.md

@@ -6,6 +6,8 @@ This guide assumes you have a already configured `commitlint` for local usage.
 
 Follow the [Getting Started](./?id=getting-started) for basic installation and configuration instructions.
 
+## Travis
+
 ```bash
 # Install and configure if needed
 npm install --save-dev @commitlint/travis-cli
@@ -20,4 +22,57 @@ script:
   - commitlint-travis
 ```
 
+## CircleCI
+
+It's just a simple example of how CircleCI configuration file could look like to validate last commit message
+
+```yml
+version: 2
+defaults:
+  working_directory: ~/project
+  docker:
+  - image: circleci/node:latest
+
+jobs:
+  setup:
+    <<: *defaults
+    steps:
+    - checkout
+    - restore_cache:
+        key: lock-{{ checksum "package-lock.json" }}
+    - run:
+        name: Install dependencies
+        command: npm install
+    - save_cache:
+        key: lock-{{ checksum "package-lock.json" }}
+        paths:
+        - node_modules
+    - persist_to_workspace:
+        root: ~/project
+        paths:
+        - node_modules
+
+  lint_commit_message:
+    <<: *defaults
+    steps:
+    - checkout
+    - attach_workspace:
+        at: ~/project
+    - run:
+        name: Define environment variable with lastest commit's message
+        command: |
+          echo 'export COMMIT_MESSAGE=$(git log -1 --pretty=format:"%s")' >> $BASH_ENV
+          source $BASH_ENV
+    - run:
+        name: Lint commit message
+        command: echo "$COMMIT_MESSAGE" | npx commitlint
+
+workflows:
+  version: 2
+  commit:
+    jobs:
+    - setup
+    - lint_commit_message: { requires: [setup] }
+```
+
 ?> Help yourself adopting a commit convention by using an interactive commit prompt. Learn how to use `@commitlint/prompt-cli` in the [Use prompt guide](guides-use-prompt.md)