Add extra themes help to output

src/bin/bat/main.rs

@@ -205,6 +205,14 @@ pub fn list_themes(cfg: &Config) -> Result<()> {
             writeln!(stdout, "{}", theme)?;
         }
     }
+    writeln!(
+        stdout,
+        "Further themes can be installed to '{}/themes', \
+        and are added to the cache with `bat cache --build`. \
+        For more information, see:\n\n  \
+        https://github.com/sharkdp/bat#adding-new-themes",
+        config_file().to_string_lossy()
+    )?;
 
     Ok(())
 }