Contributing guide correction (narwhals-dev#706)

CONTRIBUTING.md

@@ -54,8 +54,12 @@ When you have resolved your issue, [open a pull request](https://docs.github.com
 
 Please adhere to the following guidelines:
 
-1. Start your pull request title with a [conventional commit](https://www.conventionalcommits.org/) tag. This helps us add your contribution to the right section of the changelog. We use "Type" from the [Angular convention](https://github.com/angular/angular/blob/22b96b9/CONTRIBUTING.md#type).
-2. Use a descriptive title starting with an uppercase letter. This text will end up in the [changelog](https://github.com/narwhals-dev/narwhals/releases).
+1. Start your pull request title with a [conventional commit](https://www.conventionalcommits.org/) tag. This helps us add your contribution to the right section of the changelog. We use "Type" from the [Angular convention](https://github.com/angular/angular/blob/22b96b9/CONTRIBUTING.md#type).<br>
+    TLDR:
+    The PR title should start with any of these abbreviations: `build`, `chore`, `ci`, `depr`,
+    `docs`, `feat`, `fix`, `perf`, `refactor`, `release`, `test`. Add a `!`at the end, if it is a breaking change. For example `refactor!`.
+    <br>
+2. This text will end up in the [changelog](https://github.com/narwhals-dev/narwhals/releases).
 3. Please follow the instructions in the pull request form and submit. 
 
 ## How it works