Added Pre commit hook (#161)

* added precommit hook

* add git hook to contribution

* changed .yaml

.pre-commit-config.yaml

@@ -0,0 +1,6 @@
+repos:
+  - repo: https://github.com/ambv/black
+    rev: stable
+    hooks:
+    - id: black
+      language_version: python3

CONTRIBUTING.md

@@ -178,6 +178,8 @@ pip install -e '.[dev]'
 
 - Some of the [dev-dependencies](https://github.com/jbesomi/texthero/blob/6e6b8f70432979a81a09d48826fc907adc67cba7/setup.cfg#L43) will be used by any contributor of TextHero to execute the [tests.sh](./scripts/tests.sh) locally.
 
+- execute `pre-commit install` inside your project folder in order to enable git pre commit hook. This will format your code automatically before staging them
+
 ## **IMPORTANT NOTE**
 
 - Some of the [dev-dependencies](https://github.com/jbesomi/texthero/blob/6e6b8f70432979a81a09d48826fc907adc67cba7/setup.cfg#L43) are necessary **IF** the contributor wants to update the website or run the website locally but please remember that one **shouldn't be sending these kind of changes as a Pull Request**.

setup.cfg

@@ -49,3 +49,4 @@ dev =
     nbsphinx
     parameterized>=0.7.4
     coverage
+    pre-commit