Add build instructions to README.md

[gmelodie]

[rvagg]

Might be best to point to the README in the filc directory instead? The ffi dependency needs setting up and it requires other dependencies and all those complexities are detailed in that README. And, since Makefile handles a lot of the hassle, make filc might be better advice (also in that README).

[alvin-reyes]

I suggest we add the following:

1 - build instruction

git clone <> 
cd filclient
make

2 - How to use

go get github.com/application-research/filclient@latest

followed by how to use

I discussed this with @elijaharita and he'll modify the readme.md to add these.