docs(project/COMMIT_MESSAGES): add description

docs/project/COMMIT_MESSAGES.md

@@ -0,0 +1,81 @@
+# Commit Messages
+
+Contributors should adhere to our [commit message guidelines](https://docs.google.com/document/d/1QrDFcIiPjSLDn3EL15IJygNPiHORgU1_OOAqWjiDU5Y/edit?pli=1).
+
+The goal is to achive better readability of the projects commit log and eventually use the log as a low level change tracker.
+
+```plain
+feat(context-pad): add delete button
+fix(modeling): assign valid semantic ids
+fix(viewer): correctly fire imported event
+fix(core): handle missing BPMNPlane during import
+```
+
+It is important for [semantic versioning](http://semver.org/) during releases and for project change tracking.
+
+
+## General Syntax
+
+```plain
+<what>(<component>): <present-tense-description>
+
+<longer-description>
+
+Closes #<issue-number>
+
+[BREAKING CHANGE:
+
+* migration notes ]
+```
+
+
+## Hints
+
+Consider the following hints when writing commit messages
+
+* Classify what you did
+
+   * `fix` commit fixes a bug, patches the project
+   * `feat` commit adds a feature, increases the minor version
+   * `docs` commit improves or adds documentation
+   * `refactor` commit cleans up mess in a non-api-breaking manner
+
+* State the module your change applies to
+
+   * `viewer` commit changes viewer code
+   * `context-pad` commit alters context pad
+   * `modeling/BpmnFactory` commit fixes a specific bug in the `BpmnFactory` (use in rare important cases only)
+
+* beware of public api (everything that has been blogged about on [bpmn.io](http://bpmn.io/blog))
+
+  * mark breaking public api via `BREAKING CHANGE: ...`
+
+* try not to swallow bug fixes (`fix`) in feature commits (`feat`). People may wait for a fixes forever.
+
+
+## Examples
+
+```plain
+feat(modeler): add create diagram option
+
+This commit adds the ability to create a new diagram in the modeler via
+
+Modeler#createDiagram(done)
+
+Related to #12
+```
+
+
+```plain
+fix(modeling): generate valid semantic ids
+
+IDs in XML documents must not start with a number as per XML spec.
+
+This commit changes our id generation behavior to use semantic ids that
+are prefixed with the elements type (never starts with a number):
+
+Before: asdas123se8as
+Now: StartEvent_asdas123se8as
+
+Closes #108
+```