Add contributing guide

Closes #9

CONTRIBUTING.md

@@ -0,0 +1,36 @@
+# Contributing to Larq
+
+👍 🎉 First off, thanks for taking the time to contribute! 👍 🎉
+
+**Working on your first Pull Request?** You can learn how from this _free_ series
+[How to Contribute to an Open Source Project on GitHub](https://egghead.io/courses/how-to-contribute-to-an-open-source-project-on-github).
+
+## Project setup
+
+To send a Pull Request it is required to fork Larq Zoo on GitHub.
+After that clone it to a desired directory:
+
+```shell
+git clone https://github.com/my-username/larq-zoo.git
+```
+
+Install all required dependencies for local development by running:
+
+```shell
+cd larq-zoo # go into the directory you just cloned
+pip install -e .[tensorflow] # Installs Tensorflow for CPU
+# pip install -e .[tensorflow_gpu] # Installs Tensorflow for GPU
+pip install -e .[test] # Installs all development dependencies
+```
+
+## Run Unit tests
+
+Inside the project directory run:
+
+```shell
+pytest .
+```
+
+## Code style
+
+We use [`black`](https://black.readthedocs.io/en/stable/) to format all of our code. We recommend installing it as a plugin for your favorite [code editor](https://black.readthedocs.io/en/stable/editor_integration.html).