docs: add new jenkins tutorial

Closes commitizen-tools#78

Author: woile

docs/tutorials/jenkins_pipeline.md

@@ -0,0 +1,52 @@
+# Create a new release with Jenkins Pipelines
+
+For this we are using the modern approach of [declarative pipelines](https://www.jenkins.io/doc/book/pipeline/).
+
+You must also ensure your jenkins instance supports docker.
+Most modern jenkins systems do have support for it, [they have embraced it](https://www.jenkins.io/doc/book/pipeline/docker/).
+
+```groovy
+pipeline {
+  agent {
+    any
+  }
+  environment {
+    CI = 'true'
+  }
+  stages {
+    stage('Bump version') {
+      when {
+        beforeAgent true
+        branch 'master'
+        not {
+          changelog '^bump:.+'
+        }
+      }
+      steps {
+        script {
+          useCz {
+            sh "cz bump --changelog"
+          }
+         // Here push back to your repository the new commit and tag
+        }
+      }
+    }
+  }
+}
+
+def useCz(String authorName = 'Jenkins CI Server', String authorEmail = '[email protected]', String image =  'registry.hub.docker.com/commitizen/commitizen:latest', Closure body) {
+    docker
+    .image(image)
+    .inside("-u 0 -v $WORKSPACE:/workspace -w /workspace -e GIT_AUTHOR_NAME='${authorName}' -e GIT_AUTHOR_EMAIL='${authorEmail}'") {
+        sh "git config --global user.email '${authorName}'"
+        sh "git config --global user.name '${authorEmail}'"
+        body()
+    }
+}
+```
+
+!!! warning
+    Using jenkins pipeline with any git plugin may require many different configurations,
+    you'll have to tinker with it until your pipelines properly detects git events. Check your
+    webhook in your git repository and check the "behaviors" and "build strategies" in
+    your pipeline settings.

mkdocs.yml

@@ -21,6 +21,7 @@ nav:
         - Writing commits: 'tutorials/writing_commits.md'
         - GitLab CI: 'tutorials/gitlab_ci.md'
         - Github Actions: 'tutorials/github_actions.md'
+        - Jenkins pipeline: 'tutorials/jenkins_pipeline.md'
     - FAQ: 'faq.md'
     - Exit Codes: 'exit_codes.md'
     - Third-Party Commitizen Templates: 'third-party-commitizen.md'