Improve documentation on DeezyMatch installation

[kasra-hosseini]

In the installation section, we provide different ways to install DeezyMatch. One of these methods is 2. install DeezyMatch from the source code in which a user can install DeezyMatch via:

python setup.py install

or:

pip install -v -e .

However, there is a difference between these two methods. In the latter, we use -e:

-e, --editable <path/url>   Install a project in editable mode (i.e. setuptools "develop mode")

This needs to be (briefly) explained in the documentation.

[mcollardanuy]

Done here.