Adding filter examples to the README

[eiso]

@juanjux thank you for the work on #23

Just opening an issue so that we add filter function (libuast) examples to the README because right now people will only discover it if they read the tests.

[juanjux]

Yes, I just wanted to get @manucorporat PR updated and fixed ASAP so we could work from that, I'll update the README as soon as I fix #24

[abeaumont]

This is related to bblfsh/libuast#20, xpath examples should be shared among the library and all the clients.

[juanjux]

@abeaumont definitely, just a couple commands in this project README showing what API to call and then it should link to that page see better examples of queries.

[eiso]

Agreed with @juanjux. It's just so that someone who lands on the repo can see how to use it and what function to call for it.

@mcuadros there should also probably be how to launch the server with the link to the documentation here, like you did for https://github.com/bblfsh/dashboard

[juanjux]

Fixed by #26