Add dev tools to pyproject.toml (#223)

Given that these dev tools is used to maintain the project, it makes
sense to add them as dev dependencies so that contributors don't have to
install them manually.

Tools which have been installed:
 - ruff
 - pre-commit

Author: mezuzza

CONTRIBUTING.md

@@ -2,10 +2,10 @@
 
 First off, thanks for taking the time to contribute! Contributions include but are not restricted to:
 
-- Reporting bugs
-- Contributing to code
-- Writing tests
-- Writing documents
+* Reporting bugs
+* Contributing to code
+* Writing tests
+* Writing documents
 
 The following is a set of guidelines for contributing.
 
@@ -29,9 +29,11 @@ this section.
    where `fork` is the remote name of the fork repository.
 
 **ProTips:**
+
 1. Don't modify code on the main branch, the main branch should always keep in track with origin/main.
 
    To update main branch to date:
+
    ```bash
    $ git pull origin main
    # In rare cases that your local main branch diverges from the remote main:
@@ -69,5 +71,5 @@ $ pre-commit install
 $ pre-commit run --all-files
 ```
 
-PDM uses `black` coding style and `isort` for sorting import statements, if you are not following them,
-the CI will fail and your Pull Request will not be merged.
+PDM uses `ruff` for code style and linting, if you are not following its
+suggestions, the CI will fail and your Pull Request will not be merged.