docs: Improve error message on client startup

dashboard might fail to start if the client is still initializing. This
commit adds that information to error messages if the dashboard fails to
connect to the client.

src/bin/neptune-dashboard.rs

@@ -39,7 +39,10 @@ async fn main() -> Result<()> {
         Ok(transp) => transp,
         Err(err) => {
             eprintln!("{err}");
-            bail!("Connection to neptune-core failed. Is a node running?");
+            bail!(
+                "Connection to neptune-core failed. Is a node running?  Or is the client still \
+                starting up?"
+            );
         }
     };
     let client = RPCClient::new(client::Config::default(), transport).spawn();
@@ -49,7 +52,10 @@ async fn main() -> Result<()> {
         Ok(nw) => nw,
         Err(err) => {
             eprintln!("{err}");
-            bail!("Could not ping neptune-core. Do configurations match?");
+            bail!(
+                "Could not ping neptune-core. Do configurations match? Or is the client still \
+                starting up?"
+            );
         }
     };