docs: Add commit message guidelines to CONTRIBUTING.md

Explain contributors how to craft useful commit messages.
We also use https://gitcop.com/ to enforce the formatting.

Closes #377

CONTRIBUTING.md

@@ -3,6 +3,7 @@
 By participating to this project, you agree to abide our [code of
 conduct](/CODE_OF_CONDUCT.md).
 
+
 ## Setup your machine
 
 `goreleaser` is written in [Go](https://golang.org/).
@@ -37,6 +38,7 @@ A good way of making sure everything is all right is running the test suite:
 $ make test
 ```
 
+
 ## Test your change
 
 You can create a branch for your changes and try to build from the source as you go:
@@ -53,6 +55,32 @@ $ make ci
 
 Which runs all the linters and tests.
 
+
+## Create a commit
+
+Commit messages should be well formatted.
+Start your commit message with the type. Choose one of the following:
+`feat`, `fix`, `docs`, `style`, `refactor`, `perf`, `test`, `chore`, `revert`, `add`, `remove`, `move`, `bump`, `update`, `release`
+
+After a colon, you should give the message a title, starting with uppercase and ending without a dot.
+Keep the width of the text at 72 chars.
+The title must be followed with a newline, then a more detailed description.
+
+Please reference any GitHub issues on the last line of the commit message (e.g. `See #123`, `Closes #123`, `Fixes #123`).
+
+An example:
+
+```
+docs: Add example for --release-notes flag
+
+I added an example to the docs of the `--release-notes` flag to make
+the usage more clear.  The example is an realistic use case and might
+help others to generate their own changelog.
+
+See #284
+```
+
+
 ## Submit a pull request
 
 Push your branch to your `goreleaser` fork and open a pull request against the