Update README.md, add git modules derectives

[aspanoz]

Maybe it a good idea add some help for git newbie and add command for git submodules. I'm talking about part where you say how to clone repository. Something like that:

git clone https://github.com/shaduzlabs/cabl.git
cd cabl
git submodule init
git submodule update
mkdir build && cd build

[shaduzlabs]

that's already included in the develop branch, which will hopefully be merged to master within a couple of weeks :)

[aspanoz]

Oh! My mistake :)