Validator on-boarding docs (#656)

* Add first draft of validator onboarding

* Update docs

* Add documentation link to main README

* Continue docs development

* Update book readme

* Update docs

* Allow vc to run without testnet subcommand

* Small change to onboarding docs

* Tidy CLI help messages

* Update docs

* Add check to val client see if beacon node is synced

* Add notifier service to validator client

* Re-order onboarding steps

* Update deposit contract address

* Update testnet dir

* Add note about public eth1 node

* Set default eth1 endpoint to sigp

* Fix broken test

* Try fix eth1 cache locking

* Be more specific about eth1 endpoint

* Increase gas limit for deposit

* Fix default deposit amount

lighthouse/src/main.rs

@@ -23,7 +23,10 @@ fn main() {
     let matches = App::new("Lighthouse")
         .version(crate_version!())
         .author("Sigma Prime <contact@sigmaprime.io>")
-        .about("Eth 2.0 Client")
+        .about(
+            "Ethereum 2.0 client by Sigma Prime. Provides a full-featured beacon \
+             node, a validator client and utilities for managing validator accounts.",
+        )
         .arg(
             Arg::with_name("spec")
                 .short("s")