Add a crate doc comment for floodsub
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
+//! Implements the floodsub protocol, see also the:
+//! [spec](https://github.com/libp2p/specs/tree/master/pubsub).
+
extern crate bs58;
extern crate bytes;
extern crate cuckoofilter;
