Adding CI checks with git hooks and pre-commit (pasqal-io#331)

* add pre-commit hooks

* update contributing guidelines with pre-commit usage

* fix a typo

* Remove superflous args from isort hooks

Running isort hook with --show-config arg and the verbose: true
flag shows that the pyproject.toml configuration is read and used
by the hook:

```terminal
...
{
    "profile": "black",
    "line_length": 79,
    "source": "/Users/manta/Desktop/Pulser/pyproject.toml"
}
...
```

.mypy_script

@@ -0,0 +1,2 @@
+#!/usr/bin/env bash
+mypy --config-file .mypy.ini

.pre-commit-config.yaml

@@ -0,0 +1,26 @@
+repos:
+  - repo: https://github.com/psf/black
+    rev: 22.1.0
+    hooks:
+      - id: black-jupyter
+
+  - repo: https://github.com/PyCQA/flake8
+    rev: 4.0.1
+    hooks:
+      - id: flake8
+
+  - repo: https://github.com/pycqa/isort
+    rev: 5.10.1
+    hooks:
+      - id: isort
+        name: isort (python)
+
+  # Calling mypy from a bash script, as I cannot figure out how to pass the
+  # .mypy.ini config file when using the hook at
+  # https://github.com/pre-commit/mirrors-mypy
+  - repo: local
+    hooks:
+      - id: mypy
+        name: mypy
+        entry: ./.mypy_script
+        language: script

CONTRIBUTING.md

@@ -115,3 +115,23 @@ annotations and pass the type checks from running:
 
     **Note**: Type hints for `numpy` have only been added in version 1.20. Make sure you have `numpy >= 1.20`
     installed before running the type checks.
+
+### Use `pre-commit` to automate CI checks
+
+[`pre-commit`](https://pre-commit.com/) is a tool to easily setup and manage [git hooks](https://git-scm.com/docs/githooks).
+
+Run
+
+```bash
+pre-commit install --hook-type pre-push
+```
+
+to install `black`, `isort`, `flake8` and `mypy` hooks in your local repository (at `.git/hooks/` by defaults)
+and run them automatically before any push to a remote git repository.
+If an issue is found by these tools, the git hook will abort the push. `black` and `isort` hooks may reformat guilty files.
+
+Disable the hooks with
+
+```bash
+pre-commit uninstall --hook-type pre-push
+```

requirements.txt

@@ -17,6 +17,9 @@ mypy == 0.921
 pytest
 pytest-cov
 
+# CI
+pre-commit
+
 # tutorials
 notebook
 python-igraph