fixed CONTRIBUTING.md and requirements.txt

Author: nicola-corbellini

.github/CONTRIBUTING.md

@@ -121,14 +121,10 @@ When you're ready to contribute code to address an open issue, please follow the
 
     Our continuous integration (CI) testing runs [a number of checks](https://github.com/cheshire-cat-ai/cheshire-cat-api/actions) for each pull request on [GitHub Actions](https://github.com/features/actions). You can run most of these tests locally, which is something you should do *before* opening a PR to help speed up the review process and make it easier for us.
 
-    Our CI also uses [`flake8`](https://github.com/cheshire-cat-ai/cheshire-cat-api/tree/main/tests) to lint the code base and [`mypy`](http://mypy-lang.org/) for type-checking. You should run both of these next with
+    Our CI also uses [`flake8`](https://github.com/cheshire-cat-ai/cheshire-cat-api/tree/main/tests) to lint the code base. You should run it with
 
         flake8 .
 
-    and
-
-        mypy .
-
     We also strive to maintain high test coverage, so most contributions should include additions to [the unit tests](https://github.com/cheshire-cat-ai/cheshire-cat-api/tree/main/tests). These tests are run with [`pytest`](https://docs.pytest.org/en/latest/), which you can use to locally run any test modules that you've added or changed.
 
     For example, if you've fixed a bug in `cheshire-cat-api/a/b.py`, you can run the tests specific to that module with

requirements.txt

@@ -3,3 +3,4 @@ setuptools >= 21.0.0
 urllib3 >= 1.25.3, < 2.1.0
 pydantic >= 1.10.5, < 2
 aenum >= 3.1.11
+websocket-client>=1.6.1