Add cython in list of deps and mention it in the README

[dneise]

IsidroAguadoRuesga mentioned in #31 that cython is needed to be installed.

It should be mentioned in the README and also find its way into the setup.py
https://github.com/cta-sst-1m/protozfitsreader/blob/master/setup.py#L24

[calispac]

Do we really need cython ? This, in principle, is tested by Travis.

[dneise]

Ah you are right ... i will have a look into it again.

Maybe on travis cython is somehow installed as a sub-dependency of something else .... and maybe on Isidros machine for some reason I do not understand cython was not installed .... so he had to install cython manually...

[IsidroAguadoRuesga]

Just for clarification, the pip install command output the following messages:
....
Successfully built protozfits
mkl-fft 1.0.0 requires cython, which is not installed.
mkl-random 1.0.1 requires cython, which is not installed.
Installing collected packages: protozfits
....
I think these dependencies comes from Intel libraries that use numpy. If these routines (mkl-...) will
not be used used in any SW on top of protozfits, you could bypass this dependency but just in case ...
I also include the complete output of the pip install command for more details.
Output_pip_install_for_zfitstest.txt