Fix the document CI error for polars profile command (nushell#14642)

# Description

Fix the docs repo CI build error here:
https://github.com/nushell/nushell.github.io/actions/runs/12425087184/job/34691291790#step:5:18

The doc generated by `make_docs.nu` for `polars profile` command will
make the CI build fail due to the indention error of markdown front
matters. I used to fix it manually before, for the long run, it's better
to fix it from the source code.

crates/nu_plugin_polars/src/dataframe/command/core/profile.rs

@@ -30,9 +30,13 @@ impl PluginCommand for ProfileDF {
     }
 
     fn description(&self) -> &str {
-        "Profile a lazy dataframe. This will run the query and return a record containing the materialized DataFrame and a DataFrame that contains profiling information of each node that is executed.
+        "Profile a lazy dataframe."
+    }
+
+    fn extra_description(&self) -> &str {
+        r#"This will run the query and return a record containing the materialized DataFrame and a DataFrame that contains profiling information of each node that is executed.
 
-The units of the timings are microseconds."
+The units of the timings are microseconds."#
     }
 
     fn examples(&self) -> Vec<Example> {