Include comparison to similar packages in readme.

[bifbof]

When a new person discovers our framework, it may be useful for them to compare it to similar packages
such as scikit-mobility and movingpandas. This allows us to present what we uniquely offer and point to other frameworks if we don't have what the person is looking for.

It is also an improvement in regards of a possible code peer review by pyOpenSci (see #86).

An example would be this part in the readme of scikit-mobility