src/tutorials/hole-punching: Clarify use of libp2p-lookup & server IP (#2616)

Author: winksaville

src/tutorials/hole_punching.rs

@@ -67,28 +67,53 @@
 //! ```
 //!
 //! Now let's make sure that the server is public, in other words let's make sure one can reach it
-//! through the Internet. From the dialing client:
+//! through the Internet. First, either manually replace `$RELAY_SERVER_IP` in the following
+//! commands or `export RELAY_SERVER_IP=ipaddr` with the appropriate relay server `ipaddr` in
+//! the dailing client and listening client.
+//!
+//! Now, from the dialing client:
 //!
 //! 1. Test that you can connect on Layer 3 (IP).
 //!
-//!     ``` bash
-//!     ping $RELAY_SERVER_IP
-//!     ```
+//!    ``` bash
+//!    ping $RELAY_SERVER_IP
+//!    ```
 //!
 //! 2. Test that you can connect on Layer 4 (TCP).
 //!
-//!     ``` bash
-//!     telnet $RELAY_SERVER_IP 4001
-//!     ```
+//!    ``` bash
+//!    telnet $RELAY_SERVER_IP 4001
+//!    ```
 //!
 //! 3. Test that you can connect via libp2p using [`libp2p-lookup`](https://github.com/mxinden/libp2p-lookup).
 //!
-//!     ``` bash
-//!     ## For IPv4
-//!     libp2p-lookup direct --address /ip4/$RELAY_SERVER_IP
-//!     ## For IPv6
-//!     libp2p-lookup direct --address /ip6/$RELAY_SERVER_IP
-//!     ```
+//!    ``` bash
+//!    ## For IPv4
+//!    libp2p-lookup direct --address /ip4/$RELAY_SERVER_IP/tcp/4001
+//!    ## For IPv6
+//!    libp2p-lookup direct --address /ip6/$RELAY_SERVER_IP/tcp/4001
+//!    ```
+//!
+//! The libp2p-lookup output should look something like:
+//!
+//!    ``` bash
+//!    $ libp2p-lookup direct --address /ip4/111.11.111.111/tcp/4001
+//!    Lookup for peer with id PeerId("12D3KooWDpJ7As7BWAwRMfu1VU2WCqNjvq387JEYKDBj4kx6nXTN") succeeded.
+//!
+//!    Protocol version: "/TODO/0.0.1"
+//!    Agent version: "rust-libp2p/0.36.0"
+//!    Observed address: "/ip4/22.222.222.222/tcp/39212"
+//!    Listen addresses:
+//!            - "/ip4/127.0.0.1/tcp/4001"
+//!            - "/ip4/111.11.111.111/tcp/4001"
+//!            - "/ip4/10.48.0.5/tcp/4001"
+//!            - "/ip4/10.124.0.2/tcp/4001"
+//!    Protocols:
+//!            - "/libp2p/circuit/relay/0.2.0/hop"
+//!            - "/ipfs/ping/1.0.0"
+//!            - "/ipfs/id/1.0.0"
+//!            - "/ipfs/id/push/1.0.0"
+//!    ```
 //!
 //! ## Setting up the listening client
 //!