Add comparison to Pipelines-as-Code

Closes #65.

[ci skip]

README.md

@@ -43,6 +43,7 @@ Note that this ODS Pipeline repository does not provide tasks for building, pack
 * [Architecture Decision Records](/docs/adr)
 * [Goals and Non-Goals](/docs/design/goals-and-nongoals.adoc)
 * [Relationship to Jenkins Shared Library](/docs/design/relationship-shared-library.adoc)
+* [Comparison to Pipelines-as-Code](/docs/comparison-pipelines-as-code.adoc)
 
 ## Compatibility
 

docs/comparison-pipelines-as-code.adoc

@@ -0,0 +1,22 @@
+# Comparison to Pipelines-as-Code
+
+The following details some similarities and differences between ODS Pipeline and link:https://github.com/openshift-pipelines/pipelines-as-code[Pipelines-as-Code]. It is not intended to suggest one or the other but to serve as a starting point to compare the two. The information used in the comparison was last updated on 2023-10-13. 
+
+## Similarities
+
+* Built on top of Tekton / OpenShift Pipelines
+* Allow to define pipelines in the source code repository
+* Trigger pipeline runs in response to Git push and other events in the version control server
+* Report status of pipeline run back to the version control server
+
+## Differences
+
+* ODS Pipeline only works with Bitbucket Server, whereas Pipelines-as-Code works with Gitlab and GitHub as well
+* Pipelines-as-Code is installed as part of OpenShift Pipelines, whereas ODS Pipeline is link:https://github.com/opendevstack/ods-pipeline/blob/master/docs/installation.adoc#installation-instructions[offered as a Helm chart]. ODS Pipeline does not use any CRDs which means it can be installed without being cluster admin.
+* For Pipelines-as-Code, the definition of a pipeline run is a full `PipelineRun` YAML resource. ODS Pipeline cuts boilerplate by allowing to specify only the link:https://github.com/opendevstack/ods-pipeline/blob/master/docs/ods-configuration.adoc#configuring-pipeline-tasks[tasks of the pipeline to run].
+* ODS Pipeline comes with opinionated link:https://github.com/opendevstack/ods-pipeline/blob/master/docs/task-start.adoc[start] and link:https://github.com/opendevstack/ods-pipeline/blob/master/docs/task-finish.adoc[finish] tasks that do quite some plumbing (Git clone, setting Bitbucket status, interaction with Nexus etc.). These tasks are automatically added to each pipeline run.
+* ODS Pipeline allows to link:https://github.com/opendevstack/ods-pipeline/blob/master/docs/ods-configuration.adoc#configuring-pipeline-triggers[configure task parameters based on triggers], e.g. allowing to have the same pipeline executed for different branches, but with different parameters.
+* ODS Pipeline ships with a built-in concept of "pipeline run artifacts", which allow to retain information about tasks (e.g. executed unit tests, SBOM files etc) in Nexus.
+* Based on the "pipeline run artifacts" concept, ODS Pipeline offers a turnkey solution to promote applications from one environment to the other. This functionality is implemented in the start and finish tasks. Users can configure a promotion chain (e.g. DEV -> QA -> PROD) which then moves built artifacts such as container images from one environment to the other. See the link:https://github.com/opendevstack/ods-pipeline/blob/master/docs/example-project.adoc[Example Project] for more details.
+* ODS Pipeline provides two Go packages, link:https://pkg.go.dev/github.com/opendevstack/ods-pipeline/pkg/tektontaskrun[tektontaskrun] and link:https://pkg.go.dev/github.com/opendevstack/ods-pipeline/pkg/odstasktest[odstasktest], for testing (any) Tekton tasks in a KinD cluster.
+* Pipelines-as-Code allows to link:https://pipelinesascode.com/docs/guide/repositorycrd/#concurrency[configure a concurrency limit] per repository, while ODS Pipeline has a link:https://github.com/opendevstack/ods-pipeline/issues/534[fixed limit of one pipeline run] per repository at a time.