Add --staking flag (#1641)

## Issue Addressed

Closes #1472 

## Proposed Changes

Add `--staking` ~~and`staking-with-eth1-endpoint`~~ flag to improve UX for stakers.


Co-authored-by: Paul Hauner <paul@paulhauner.com>

beacon_node/src/cli.rs

@@ -193,6 +193,19 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
                 .takes_value(true),
         )
 
+        /*
+         * Standard staking flags
+         */
+
+        .arg(
+            Arg::with_name("staking")
+                .long("staking")
+                .help("Standard option for a staking beacon node. Equivalent to \
+                `lighthouse bn --http --eth1 `. This will enable the http server on localhost:5052 \
+                and try connecting to an eth1 node on localhost:8545")
+                .takes_value(false)
+        )
+
         /*
          * Eth1 Integration
          */