Add pull request template (#95)

Copied and adapted from
https://github.com/vivid-planet/comet/blob/main/.github/pull_request_template.md.

.github/pull_request_template.md

@@ -0,0 +1,102 @@
+<!--
+
+PLEASE MAKE SURE TO KEEP THE PR SIZE AT A MINIMUM!
+Smaller PRs are easier to review and tend to get merged faster.
+Unrelated changes, refactorings, fixes etc. should be made in separate PRs.
+
+--->
+
+## Description
+
+<!--
+
+The description should describe the change you're making.
+It will be used as the commit message for the squashed commit once the PR gets merged.
+Therefore, make sure to keep the description up-to-date as the PR changes.
+
+PLEASE DESCRIBE WHY YOU'RE MAKING THE CHANGE, NOT WHAT YOU'RE CHANGING.
+Reviewers see what you're changing when reviewing the code.
+However, they might not understand your motives as to why you're making the change.
+
+Your description should include:
+-   The problem you're facing
+-   Your solution to the problem
+-   An example usage of your change
+
+--->
+
+<!--
+
+Everything below this is intended to help ease reviewing this PR.
+Remove all unrelated sections.
+
+WHEN MERGING THE PR, REMOVE THIS FROM THE COMMIT MESSAGE.
+
+-->
+
+## Example
+
+<!--
+
+Make sure to provide an example of your change if your change includes a new API.
+You can update the [example config](https://github.com/vivid-planet/dev-process-manager/blob/main/example/dev-pm.config.js) to do so.
+
+--->
+
+[ ] I have verified if my change requires an example
+
+## Changeset
+
+<!--
+
+When making a notable change, make sure to add a changeset.
+See [CONTRIBUTING.md](https://github.com/vivid-planet/comet/blob/HEAD/CONTRIBUTING.md) for more information.
+
+TL;DR
+
+Add a changeset when:
+-   changing the package's public API (`src/index.ts`)
+-   fixing a bug
+-   making a visual change
+
+Changeset writing guidelines:
+-   Use active voice: "Add new thing" vs. "A new thing is added"
+-   First line should be the title: "Add new alert component"
+-   Provide additional information in the description
+-   Use backticks to highlight code: Add new `Alert` component
+-   Use bold formatting for "headlines" in the description: **Example**
+
+--->
+
+[ ] I have verified if my change requires a changeset
+
+## Related tasks and documents
+
+<!--
+
+Link to related tasks and documents, for instance, https://vivid-planet.atlassian.net/browse/COM-XXX.
+
+MAKE SURE THAT EVERYTHING REQUIRED TO UNDERSTAND YOUR CHANGE IS IN THE PR DESCRIPTION.
+Reviewers shouldn't need to review tasks, JIRA conversations etc. to understand what you're doing.
+
+-->
+
+## Open TODOs/questions
+
+<!--
+
+-   [ ] Need to validate that this actually works
+-   [ ] Merge parent PR
+
+-->
+
+## Further information
+
+<!--
+
+Further information that helps reviewing the PR, for instance:
+-   Alternative solutions you have considered
+-   Dependent PRs
+-   Links to relevant documentation, blog posts etc.
+
+-->