Update CONTRIBUTING.md (#95)

This PR enhances the contribution guide, by:
- Adding a reference to project roadmap
- Adding considerations about commit messages and self-documented code

CONTRIBUTING.md

@@ -12,6 +12,14 @@ Issues and feature requests
 If you have any issues to report or features to request, please use the
 [issue tracker](https://github.com/protofire/solhint/issues).
 
+### Roadmap
+
+There's a (tentative) [roadmap](ROADMAP.md) in which we've put down what we envision to be the best-next functionalities.
+
+Since the project is constantly evolving and new features are requested/discovered as we go, this roadmap is open for discussions and we expect it to change over time.
+
+Roadmap-wise contributions via new issues are always welcomed.
+
 Development
 -----------
 
@@ -74,6 +82,9 @@ All code changes happen through pull requests. To create one:
 3. Ensure the tests are still passing. Please remember to add tests for new features.
 4. Create the pull request.
 
+### Considerations
+- It is highly encouraged to follow [The seven rules of a great Git commit message](https://chris.beams.io/posts/git-commit/#seven-rules)
+- Code should be self-documented. But, in case there is any code that may be hard to understand, it must include some comments to make it easier to review and maintain later on.
 
 License
 -------