Add build instructions to README.md

[gmelodie]

No description provided.

[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.

[elijaharita]

Suggested change

	make
	cd filc
	go build
	make filc

any reason not to just mention this, since we already have it?

[elijaharita]

we should probably add some info about the filecoin-ffi setup process

Suggested change

	go get github.com/application-research/filclient@latest
	go get github.com/application-research/filclient@latest
	# Add filecoin-ffi as an extern dependency
	git clone https://github.com/filecoin-project/filecoin-ffi extern/filecoin-ffi
	cd extern/filecoin-ffi
	git checkout [filclient's dependency version]
	make
	cd ../..
	go mod edit -replace github.com/filecoin-project/filecoin-ffi=./extern/filecoin-ffi

this process is really terrible and i wish we could do something about it