Add quotes to pip package name for shell support

[ehenoma]

ZSH does not support the current command. By adding quotes to the package name it works.

[t-huyeng]

I can confirm that the current pip install deutschland[jobsuche] does not work for ZSH and that it is working with pip install 'deutschland[jobsuche]'

However, I do not think that changing python-client/README.md is a good solution as it may be overwritten by a new generation of the python-client folder. It may also break compatibility with other shells.

If we want to add the a ZSH command it should be done inside the template