Add info about development environment into CONTRIBUTING.md (#110)

CONTRIBUTING.md

@@ -8,6 +8,55 @@ the developers managing and developing this open source project. In return,
 they should reciprocate that respect in addressing your issue or assessing
 patches and features.
 
+## Development environment
+
+Next steps should work on clear Ubuntu 18.04.
+
+- Install necessary dependencies:
+
+```sh
+$ sudo apt-get install -y curl redis-server python3-dev python3-pip python3-venv libldap2-dev libsasl2-dev
+```
+
+- Install [Visual Studio Code](https://code.visualstudio.com/docs/setup/linux#_debian-and-ubuntu-based-distributions) for development
+
+- Install CVAT on your local host:
+
+```sh
+$ git clone https://github.com/opencv/cvat
+$ cd cvat && mkdir logs keys
+$ python3 -m venv .env
+$ . .env/bin/activate
+$ pip install -U pip wheel
+$ pip install -r cvat/requirements/development.txt
+$ python manage.py migrate
+$ python manage.py collectstatic
+```
+
+- Create a super user for CVAT:
+
+```sh
+$ python manage.py createsuperuser
+Username (leave blank to use 'django'): ***
+Email address: ***
+Password: ***
+Password (again): ***
+```
+
+- Run Visual Studio Code from the virtual environment
+
+```
+$ code .
+```
+
+- Inside Visual Studio Code install [Debugger for Chrome](https://marketplace.visualstudio.com/items?itemName=msjsdiag.debugger-for-chrome) and [Python](https://marketplace.visualstudio.com/items?itemName=ms-python.python) extensions
+
+- Reload Visual Studio Code
+
+- Select `CVAT Debugging` configuration and start debugging (F5)
+
+You have done! Now it is possible to insert breakpoints and debug server and client of the tool.
+
 ## Branching model
 
 The project uses [a successful Git branching model](https://nvie.com/posts/a-successful-git-branching-model).