Add python3-gdbm as dependencies

[ikus060]

I need to install the following package to make it work.

sudo apt-get install python3-gdbm

[ghost]

I'm running ubuntu 17.04, and for me it needs gir1.2-webkit-3.0

Whereas I don't need to install python3-gdbm

Thanks.

[fossfreedom]

readme updated. thanks