Remove flake8 in favor of ruff

CONTRIBUTING.md

@@ -45,16 +45,17 @@ pytest tests/test_<file_name>.py::test_<method_name>
 
 ### 2. Test if your code is PEP8 compliant
 
-#### Run Flake8
+#### Run Ruff
 
 ```bash
-flake8 freqtrade tests scripts
+ruff .
 ```
 
-We receive a lot of code that fails the `flake8` checks.
+We receive a lot of code that fails the `ruff` checks.
 To help with that, we encourage you to install the git pre-commit 
-hook that will warn you when you try to commit code that fails these checks. 
-Guide for installing them is [here](http://flake8.pycqa.org/en/latest/user/using-hooks.html).
+hook that will warn you when you try to commit code that fails these checks.
+
+you can manually run pre-commit with `pre-commit run -a`.
 
 ##### Additional styles applied