Contributing guide: clean up and improve

Author: UweTrottmann

CONTRIBUTING.md

@@ -1,21 +1,26 @@
-Contributing
-============
+# Contributing
 
-**Note:** [This work](README.md) is licensed under the [Apache License 2.0](LICENSE.txt).
-If you contribute any [non-trivial](http://www.gnu.org/prep/maintain/maintain.html#Legally-Significant) patches make sure to read and agree with the license.
+## Would you like to contribute code?
 
-#### Would you like to contribute code?
+**Note:** [This work](README.md) is licensed under the [Apache License 2.0](LICENSE.txt).
+If you contribute any [non-trivial](http://www.gnu.org/prep/maintain/maintain.html#Legally-Significant) patches make 
+sure to read and agree with the license.
 
 **Note:** Keep your pull requests small, otherwise it is less likely they will get merged.
 
+**Note:** This project is built with [Maven](https://maven.apache.org/), see the `pom.xml` in the root folder.
+
 1. [Fork tmdb-java](https://github.com/UweTrottmann/tmdb-java/fork).
-2. Create a new branch and make [great commits + messages](http://robots.thoughtbot.com/post/48933156625/5-useful-tips-for-a-better-commit-message). If you add or modify methods, make sure to also create and run basic tests (see `src/test`).
-3. [Start a pull request](https://github.com/UweTrottmann/tmdb-java/compare) against `main`.
+2. Create a new branch and make great commits + messages:
+
+   * Each line should be 72 characters or less.
+   * Add a subject line and body text separated by an empty line.
+   * Describe why this change, how does it address an issue or what side effects it has.
+   * Link related issues or documentation as needed. 
 
-#### No code!
-* You can [discuss or submit bug reports](https://github.com/UweTrottmann/tmdb-java/issues)!
+3. If you add or modify methods, make sure to also create and run basic tests (see `src/test`).
+4. [Start a pull request](https://github.com/UweTrottmann/tmdb-java/compare) against `main`.
 
-Setup
------
+## No code!
 
-This project is built with [Maven](https://maven.apache.org/), see the `pom.xml` in the root folder.
+You can [discuss or submit bug reports](https://github.com/UweTrottmann/tmdb-java/issues)!