missing system requirements in README

[alexandervlpl]

I want to run Photon myself instead of abusing your excellent API. :)

It would be really helpful to see system requirements somewhere, so I can immediately pick the right hosting solution!

[oberhamsi]

you only need java 8. photon can work with an external elasticsearch cluster but will start its own instance by default.

[otbutz]

can work with an external elasticsearch cluster

Would be good to know which versions of ES are supported though.

[oberhamsi]

it's packaged with elastic 5.5. so every elastic that is compatible with that one should work. i'm only familiar with 1.x and 7.x so i can't really say.

[alexandervlpl]

I actually meant hardware requirements. I have this running very well with 16GB RAM, SSD, 2.1Ghz Intel Xeon (4 core).

Maybe we can establish and document a minimal setup?

[lonvia]

Duplicate of #523.