Give the "unset user" warning a trailing newline.

At the moment, the unset user warning is lacking a trailing newline, so
we end up printing anything else that's output directly on the same line.

CHANGELOG.md

@@ -123,6 +123,7 @@ Thanks to the people who made this release happen!
  * Waleed Khan (@arxanas)
  * Sean E. Russell (@xxxserxxx)
  * Pranay Sashank (@pranaysashank)
+ * Luke Granger-Brown (@lukegb)
 
 
 ## [0.5.1] - 2022-10-17

src/cli_util.rs

@@ -903,7 +903,8 @@ impl WorkspaceCommandHelper {
         {
             ui.write_warn(r#"Name and email not configured. Add something like the following to $HOME/.jjconfig.toml:
   user.name = "Some One"
-  user.email = "someone@example.com""#)?;
+  user.email = "someone@example.com"
+"#)?;
         }
         Ok(())
     }